If you have this error, it means that your web server needs a bigger amount of php memory size allocated for your website. Your web server will attribute to each site which it hosts a certain amount of memory. What you need to do is to increase the memory limit for your installation.
The most common error message that you get when the memory size is exhausted is:
Fatal error: Allowed memory size of xxxxxxxx bytes exhausted (tried to allocate xxxxxxxx bytes) in /your website/public_html/wp-includes/plugin.php on line xx
Connect to your server via FTP and edit the wp-config.php file and add the following line:
If the solution above won’t work, most probably your hosting service is overwriting the setting your add in wp-config.php from the global server settings. Please contact your hosting company and ask them to help you, they will know what to do in this case.