Look for a new OS and an upgrade to FM13. Windows XP is now 13 years old. Peer-to-peer was never meant to be "server lite", so FMP/FMPA11 are not optimized to run unattended, nor should they be.
But if you want to try and band-aid it, try writing some automated tasks to reboot your system once a week, and auto-launch the database when it comes back up.
You're already risking major corruption by killing the process, and by hosting peer-to-peer as a server without regular backups (note, if you are backing up the file when it's in use, you may also be corrupting it that way).
Basic filemaker hosting is relatively cheap (~$30/month), that might be a good option for this office. FM11 hosting still exists, so you wouldn't even have to upgrade.
As for potential causes, make sure the "disconnect from server when idle" box is checked in the privilege set the accounts are on, failure to do so can cause "ghost" sessions when things like DHCP IP address changes occur.
The last time I set up peer-to-peer for a small office was back in FM5 days, and I set up their host OS to shut down in the middle of the night and reboot an hour later with the FMP files set to open on reboot. That kept ghost sessions from being an issue when users failed to quit the program properly, or related files stayed open in the background.
I discourage peer-to-peer in general. Is the cost of FMServer really so much more than their data is worth to them? P2P will eventually lead to corrupt data...maybe not in 100% of the cases, but certainly in way too many to justify the risk. Why FMI still supports P2P when FMS is dirt cheap for developer testing is beyond me.
There is no good reason for this, even on Windows XP
Note: you can end up with "ghost" clients even on FileMaker Server
Restart is the only "fix", so it is unfortunate that the host locked up
Be sure to backup often
Just out of curiosity, run a Recover on the file, and check the log for any items "changed"
Thanks Stephen and Everybody for their comments.This company has used the peer-to-peer solution over years and is not willing to invest into the FM Server. At least I can set up a re-boot routine, so thanks again for your comments!
I would certainly make them sign something in writing that makes them accept the risks they are taking. When it does go bad, it could get ugly, and you'll want to protect yourself.
"Proactive, not reactive" is a good motto to have.