Stan,

> The error always happens in the same place in the code:

Which function returns this?

> I am using the default transaction settings (snapshot,
> write I think).

If this happens on the heavy load only, you should be very
careful about how do you manage transactions. What TPB parameters
do you supply for 'isc_start_transaction'?

> Each client is inserting 1 record into 8 tables followed
> by an update on 2 of the records that were just inserted.
> This operation is done in a single transaction. I have tried
> separate transactions, but had the same result.

Keep it single transaction.

> At the same time other clients are selecting from these tables.

If they are reading only - do it within read-only transcation.
What TPB parameters do you supply for 'isc_start_transaction' in
this case?

Make sure that you commit(rollback) transactions as soon as possible.

--

I also have a problem using Firebird with CGI on Windows XP SP2:

If my C++ CGI application works with a local embedded firebird
database residing in the same cgi-bin directory, then no problem -
I can use my browser to work with a database.

However if my CGI application tries to connect to Firebird server
running on the same machine - then there is a problem "SQL error:
unavailable database"

How did you manage to setup CGI with Firebird?

Regards,
Glebas