Cannot login - Login page freezes - Elgg 2.3.16

Suddenly users cannot login. The login page freezes and after a few seconds it says "Page unresponsive"
In the error log I have: Got error 'Primary script unknown', referer:
My Elgg site address is under
I checked through the FTP and there is no page like this
What might be the reason for this strange bug.
How to fix?
Thank you very much