nessusd.messages file disappearing

[Fire Wall]

Greetings!

I'm having a problem when I run a scan against a large number of hosts 
(e.g., 1200 hosts).

It seems that my nessusd.messages file disappears when the scan 
completes.  I've logged on while the server is running the scan and have 
noticed that the nessusd.messages file is over a hundred megs in size.  The 
file system has over 500 megs.

Is there a size limit to the nessusd.messages file?  Any idea what could be 
causing this to disappear.  It works fine when I only scan one or two hosts.

Joel