This is not a problem I have personally experienced, but I thought I would throw it out here and see if anybody else has.
I just got a call from a police officer back east. He says they have several DS2 DVRs that will have the monitor image just freeze. It still seems to work just fine using the Net-Vu software even when the monitor image is frozen. Its not a signal loss freeze. The monitor output just locks up, but you can connect via netwrok and perform all functions.
I don't install that many DM units. However I did have one that acted like that. DM doesn't use a real OS. It does have open ports that real computers can try to exploit. It wasn't the DM unit that was at fault, but there was a virus/worm going nuts on the network it was attached to. The other virus/worm infected computers on the network were pinging the open DM ports into the ground. I'd see what version he has and if there was some update from DM that might fix it for him. Here is a place to look to be more sure what the problem is. (From the instruction manual) The Logfile stores all information on every action that is carried out by the Digital Sprite 2; when alarms are received and actioned, resets, failed outward bound alarm connections, etc. This is the current file and will continue to store data until it reaches its maximum size limit (typically
1Mb). This file then writes over the top of the Logfile Backup and becomes the backup file and a new logfile is created. This ensures current and recent information is always available. The information detailed is; Time and date, Reset Code and Reason, Connection-status, Site and ARC ID. This is an example of the details that are contained in the logs; this shows an unauthorised user trying to access the Digital Sprite 2 using an FTP connection.