Looks like this is an OS/settings problem. :S
Tried on an other server and it works fine.

--- In firebird-support@yahoogroups.com, "ma_golyo" <ma_golyo@...> wrote:
>
> Hi!
>
> Cannot connect to server under heavy load.
> I get "connection rejected by remote interface" (335544421).
>
> Is this a bug, ot there is an option in firebird.conft to avoid this?
>
>
> Firebird.log (FB20 Classic Server)
> L3S-4 Wed Oct 24 14:04:28 2012
> I/O error for file "C:\PROGRAM FILES\FIREBIRD\FIREBIRD_2_0\SECURITY2.FDB"
>
>
> L3S-4 Wed Oct 24 14:04:28 2012
> lock conflict on no wait transaction
>
>
> L3S-4 Wed Oct 24 14:04:32 2012
> Error while trying to access file
>
>
> L3S-4 Wed Oct 24 14:04:32 2012
> no permission for read-write access to database C:\PROGRAM FILES\FIREBIRD\FIREBIRD_2_0\SECURITY2.FDB
>
>
> L3S-4 Wed Oct 24 14:04:36 2012
> The process cannot access the file because it is being used by another process
>