Fatal error

After instalLation, when I try go to plugin’s setting page, i get this message:

Fatal error: Call to undefined function get_current_screen() in /home/xxxxx/domains/mysite.com/public_html/wp-content/plugins/ninja-forms/includes/admin/display-screen-options.php on line 7

And this on my site’s main page:

Fatal error: Call to undefined function is_main_query() in /home/xxxxxx/domains/mysite.com/public_html/wp-content/plugins/ninja-forms/includes/display/form/display-form.php on line 27

Any solution?!

http://wordpress.org/extend/plugins/ninja-forms/