> I have my proprietary udf library and it is working with FB 1.5.x superserver but is not working with classic server. Any select
> which uses some function from my library results in:
>
> *** IBPP::SQLException ***
> Context: Database::Statistics
> Message: isc_database_info failed
>
> SQL Message : -902
> Unsuccessful execution caused by a system error that precludes
> successful execution of subsequent statements
>
> Engine Code : 335544721
> Engine Message :
> Unable to complete network request to host "localhost".
> Error writing data to the connection.
> An existing connection was forcibly closed by the remote host.
>
> And the firebird.log contains:
> MYNAME (Client) Mon Mar 22 08:49:49 2010
> INET/inet_error: send errno = 10054
>
> Nothing like this happens (even on classic server) when I am issuing select that uses function from library supplied with Firebird
> installation like ib_udf.dll.

Because ib_udf does not cause problems, it is obvious that problem is in your library.
But it is impossible to tell what is wrong if you do not show us the code.