Errror in extension install process

[gc1983]

Hi,

when i try to activate any extension i receive this message:
call_user_func_array() expects parameter 1 to be a valid callback, class ‘X_Validation_Cornerstone’ does not have a method ‘ajax_install_plugin’

[gc1983]

I manually deleted the revslider dir in plugin directory.

now the err message is
Warning: call_user_func_array() expects parameter 1 to be a valid callback, class ‘X_Validation_Cornerstone’ does not have a method ‘ajax_install_plugin’ in membri/sito/wp-includes/class-wp-hook.php on line 286

Warning: Error while sending QUERY packet. PID=12507 in /membri/sito/wp-includes/wp-db.php on line 1924
{“success”:true,“data”:{“plugin”:“revslider/revslider.php”}}

[friech]

Hi There,

Thank you for writing in, can you confirm that you are fully updated? (Theme and Plugins)

You can find the latest version numbers here: (https://theme.co/apex/forum/t/troubleshooting-version-compatibility/195) Then you can compare them to what’s installed on your site.

If you find anything to be out of date, you can review our update guide.

If that did not work, please provide us login credentials (/wp-admin and FTP) on a secure note so we can take a closer look.

Cheers!