Line 1287 refers to writing to the system event log.
Maybe it’s so huge it’s running into problems inserting the event into the modx_event_log table in the Database.
If you have PHPMyAdmin access I’d have a look that table.
Thanks for your reply!
I have already truncated the "modx_event_log" table (also the "modx_manager_log").
But nothing happens. Still the same issue...
At this point, I would try to raise the php memory_limit. Your host tech support may do it for you, or you can try putting that in a custom php.ini.
This type of thing: