Thank you very much.   I will try the  -o switch and the gfix suggestion as well.

Don't bother with gfix.  It does a physical database check - pointers point to what
they should, pages are the right type, etc.  Your problem is with the logic of the database,
specifically with one of the grants.  

From a very historical point of view, InterBase was created with a security model that
everything was allowed unless prohibited.  SQL's model is that nothing is allowed
unless permitted.  Some odd things were done to convert from the InterBase model
to the SQL model and not all of them were done well.  You seem to have tripped over
one of those issues, probably something that worked OK with earlier versions of
Firebird, but which contemporary Firebird rejects. 

Good luck,

Ann