I'm having the exact same issue...all scripts are named, saved, and in the solution. Save All, close SSMS, reopen--get error reported by OP. Only one of the scripts tabs is...
Alternatively, you could simply define a composite foreign key constraint with a "hidden" persisted computed column, defining the subset of regions which are valid references for the office table.
I was searching for the 2005 replace for syscomments and found this thread. I see it's fairly old, but figured I'd post the solution I've just worked up this afternoon....