I am running firebird 2.5.1 super-classic on ubuntu server 12.04

Firebird/linux AMD64 (access method), version "LI-V2.5.1.26351 Firebird 2.5"
on disk structure version 11.1

The problem I am experiencing is that Firebird randomly hangs every
couple of days, I need to do a service restart to get it going again,
all I see in the logs is this:

ubuntufirebird Tue Sep 18 09:18:49 2012
Shutting down the server with 3 active connection(s) to 1
database(s), $

ubuntufirebird (Client) Tue Sep 18 09:18:52 2012
/usr/sbin/fbguard: /usr/sbin/fb_smp_server killed (did not
terminate)

ubuntufirebird (Client) Tue Sep 18 09:18:52 2012
/usr/sbin/fbguard: guardian starting /usr/sbin/fb_smp_server

Any suggestions please?

Thanks
Gary