I attach to 2 separate databases on the same machine in quick succession via localhost. Firebird always opens the first database with no problems but often hangs opening the second database. The only way out is to kill and restart fbserver as subsequent attempts to reattach to the first database fail. Once it works correctly It then continues through the session to attach without error to both databases repeatedly whenever my program is re-started. On shutting down and later reboot firebird often hangs again. Debugging shows my program stops on calling isc_attach_databaseType. System and firebird logs show nothing that I can see as relevant.

I have tried all 32/64 versions of Firebird for OSX except the lipo version and they all exhibit the same problem in Lion.
I have also had similar hang on detaching from a single database on two occasions.

I have tried a trace/audit but get the message that there are no plugins loaded.