Cant Log into WordPress pannel

okay so this error showed up on our site yestarday at first i was able to get on the wordpress pannel but hours later it completley stop working

here are the errors

Warning: session_start() [function.session-start]: Cannot send session cookie – headers already sent by (output started at /home/sinciara/public_html/wp-includes/default-filters.php:198) in /home/sinciara/public_html/wp-content/plugins/category-icons/category_icons.php on line 47

Warning: session_start() [function.session-start]: Cannot send session cache limiter – headers already sent (output started at /home/sinciara/public_html/wp-includes/default-filters.php:198) in /home/sinciara/public_html/wp-content/plugins/category-icons/category_icons.php on line 47

and now are ftp is locked
if anyone can help please