>I have had three occurrences (on one of my own servers) since our
> upgrade from FB 2.0 to FB 2.1.1 where suddenly the server (superserver
> on windows, using local/xnet connections) stops accepting new database
> attachments or service attachments.
>
> isc_attach_database() fails and reports -904 (unsuccessful execution
> caused by an unavailable resource) with specific engine code 335544375
> and message 'unavailable database' (of course).
>
> At the time of this starts happening the log shows :
>
>
> TIP (Server) Sun Aug 17 21:21:38 2008
> XNET error: get_free_slot() failed
>
> TIP (Server) Sun Aug 17 21:21:38 2008
> Database:
> unknown ISC error 0
>
>
> To cure it, a simple stop of the superserver service, followed by a
> start is enough. So the server process is still responsive. It looks
> like people with existing connections are not impaired until of course
> they try to open new attachments.

Looks like http://tracker.firebirdsql.org/browse/CORE-1902, but that
case was for Super Classic...

How many your clients may connect at the same second simultaneously ?
Does a little pause between connection attempts (if its possible) helps ?

Of course, reproducible test case will help to resolve issue.

Regards,
Vlad