Fatal Error after enabling add on

Hi there,

I have just installed GeneratePress and added the GP Premium plugin. Successfully enabled first two add ons, but when I clicked 'enable' for Header add on the following error appeared:

Warning: require_once(/home/she16532/public_html/wp-includes/class-wp-image-editor.php) [function.require-once]: failed to open stream: No such file or directory in /home/she16532/public_html/wp-content/plugins/gp-premium/addons/generate-page-header/inc/bfi_thumb.php on line 103

Fatal error: require_once() [function.require]: Failed opening required '/home/she16532/public_html/wp-includes/class-wp-image-editor.php' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home/she16532/public_html/wp-content/plugins/gp-premium/addons/generate-page-header/inc/bfi_thumb.php on line 103

I can no longer access my dashboard or site at http://shellbalogh.com/

Are you able to help resolve this? I haven't edited the code on line 103 at all?

Thanks!