Why is everyone else not having this problem?  The databases are Firebird databases.  For 15 years we had no corruption from Interbase 6.  Two years ago, we backed up our databases with Interbase 6 gbak and then used Firebird 2.52 to restore them. 

Firebird 2.52 will back them up, but will not restore them without getting the "trigger (3)" error.  Since we have 5 databases, each built by Firebird two years ago from Interbase 6 backups and backed up for two years by Firebird 2.52 gbak, and totally different programs accessing the databases, it appears the corruption is/has been caused by Firebird.

Yet, no one else has seen this problem?  

The problem may be that InterBase 6 and older Firebirds still used some non-SQL style grants.  Over time,
Firebird has become fussier about correct syntax and semantics.   If you still have an old database, perhaps
you can look at the privileges especially those on system tables.

Good luck,

Ann