phpMyAdmin isn’t quite helpful when it comes to error management and outputs, however if you hit into phpMyAdmin – Error: Token Mismatch, like in the screenshot below:
The solution is quite easy and it’s usually related to quota. The same solution applies for a 401 – Access Denied(if it’s a cPanel 11.44+ server):
401 - Access Denied
Unable to establish a PHP session.
If you believe that this is in error or inadvertent, contact your system administrator and ask them to review your server settings.
Verify the account’s quota and make sure it hasn’t reached the limit.
If there’s no problem with the quota you should check /tmp partition and make sure it’s not full along with the session.save_path variable in PHP:
session.save_path = /tmp
If /tmp has enough disk space you should check its permissions and make sure the account in question is allowed to create session files in that folder.