Cannot save form data

The error message is below. Haven’t tried to reproduce it but:

  • These databases are a copy of the original. After that I uploaded four new revisions to the solution and, with that, did some updates to the tables too…

Could the problem be there? Because: I don’t have the problem on my developer machine (although this is the original database also) and I don’t have the issue on my other server (and this is a fresh database)…

BTW I do have a primary key for every table…