The cause: The reason for the fatal error: allowed memory size of 268435456 bytes exhausted is that the PHP back-end of Plesk exceeds the memory limit. This could occur if the thing being operated on has a complicated structure.

Solution:

Solution for Plesk on Linux

1. By using SSH, connect to the Plesk server.
2. Open a text editor and the php.ini settings file for Plesk. We are use the vi editor in this example:

             # vi /usr/local/psa/admin/conf/php.ini

3. Raise the memory_limit limit to 512

4. Save the modifications then close file

5. The Plesk management service to be restarted:

# service sw-engine restart && service sw-cp-server restart

6. Retry the unsuccessful procedure you just did. Restart the services and increase the memory_limit limit if it continues to fail with the same problem.

7. Replace the following line in /etc/cron.daily/50plesk-daily using a text editor to stop the        modifications from being undone during the Plesk update:

-On CentOS/RHEL-based, use with:

/ usr / local / psa / bin / sw-engine-pleskrun /usr/local/psa/admin/plib/DailyMaintainance/script.php> / dev / null 2> & 1 && sed -i '/ memory_limit / cmemory_limit = 512M' /usr/local/psa/admin/conf/php.ini

-On Debian/Ubuntu-based, use with:

/opt/psa/bin/sw-engine-pleskrun /opt/psa/admin/plib/DailyMaintainance/script.php >/dev/null 2>&1 && sed -i '/memory_limit/cmemory_limit = 512M' /usr/local/psa/admin/conf/php.ini

Solution for Plesk on Windows Server

1. Utilize RDP to establish a connection to the Plesk server.
2. In a text editor, open the  %plesk_dir%adminconfphp.ini file for Plesk PHP.
3. Raise the memory limit level to 512.
4. Close the file after saving the modifications.
5. Restart the Plesk management service:
   Launch PowerShell and execute each command individually:
   PS import-module WebAdministration
net stop “Plesk PopPass Service”
net stop “Plesk Management Service”
net start “Plesk Management Service”
net start “Plesk PopPass Service”
Restart-WebAppPool PleskControlPanel
6. Retry the unsuccessful operation. Adjust the memory_limit value to a higher number and restart the services if it still fails with the same problem.