I bet it is a mismatch in names.
If you update the page name or apply server validation it might update the page reference in the server code, which in turn requires updating the page reference in the value references.
It is a bug of sorts, since the next version of form builder won't ever update the page reference once implemented it won't have the problem. The current version it is easy to get out of synch.
Most likely you should look in your server validation code and find where the page name reference is. Then make sure it is the same on the form itself and find/replace if it isn't.
Did this help? Tips are appreciated...
