I have a NW6.5sp5 with all post-sp5 patches that randomly hangs about once a

The server is a dedicated (low traffic) ftp server (NAT to an external IP
address via BorderManager). All that is running on the server other than
nwftpd is Brightstor Arcserve NWAGENT and Symantec Antivirus.

I get no abend - just a dead stop. Nothing in the logs. I have to shut the
thing down to restart it. Any ideas on where to start looking? Thanks!