Every night I run nbackup to dump a database in order to get streamed to tape. Recently we loaded a new database using gbak and since then, nbackup often gives me the following error:

Fatal lock manager error: invalid lock id (226944), errno: 22
--Invalid argument

I raised the following vars to no avail (doubling there values):
LockSemCount = 64
LockHashSlots = 2011

So my questions are:
- what could explain the invalid lock error?
- how to debug/analyse it (any handy tools/tricks)?
- how to prevent/fix it?

Config:
CentOS 5.5
firebird-filesystem-2.1.3.18185.0-2.el5
firebird-libfbembed-2.1.3.18185.0-2.el5
firebird-2.1.3.18185.0-2.el5
firebird-libfbclient-2.1.3.18185.0-2.el5
firebird-classic-2.1.3.18185.0-2.el5

Thanks, Mark