Error on notification

Hi,

When I submit a form I get this error and when I disable Gravity PDF I do not get this error.
What is problem with it and how to fix it?

Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: A non-numeric value encountered in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/mpdf.php on line 30441 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: A non-numeric value encountered in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/mpdf.php on line 30441 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: A non-numeric value encountered in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/mpdf.php on line 30441 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1302 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Cannot assign an empty string to a string offset in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1307 Warning: Illegal string offset ‘ID’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355 Warning: Illegal string offset ‘LANG’ in /customers/a/c/0/sitename/httpd.www/wp-content/plugins/gravity-forms-pdf-extended/vendor/blueliquiddesigns/mpdf/classes/cssmgr.php on line 1355