Dear Zd,

>
> Here is the error message from Firebird.log:
> internal gds software consistency check (invalid SEND request (167), file: exe.cpp line: 643)

That's interesting and somewhat unexpected. Internally firebird
uses an API called OSRI (Open Standard Relational Interface) that
is a set of calls and a query description language called BLR.
The client has asked the server to send it some data and the
server says (translating loosely) "I already told you there was
no more data".

Let me think about that for a bit. It's possible that a UDF
damaged something that made the server think it was at the end
of the table when it wasn't, but 1) that would be a transient
error, 2) read only requests like gbak shouldn't invoke the UDF,
and 3) that's odd.

Do save a copy of the database before you try gfix.

Best,

Ann