I just experienced this problem on a site running EE 2.3.1 and MSM 2.1.1.
In my case the site has gone completely off the air, and I can’t even login or access the CP.
It happened after an aggressive session updating banned IPs, and apparently I tripped over the limit. After a lot of sleuthing, I finally figured out what must have happened—that this data is stored with site_system_preferences and overloading the field causes truncation and system failure. Great. :-p
Is there any way to rehabilitate the site_system_preferences data directly in the db, at least enough to get back into the CP and sort out the Banned IPs so that this field no longer truncates?
Unfortunately, I don’t have a recent backup of the DB :-(
Next step will be to go to the hosting service and see if they have a backed-up state we can retrieve. But still . . .
Is there anything that can be done with the truncated field to get back up and running? Or is the only option to find some backup and go backward?