This may have nothing to do with anything, but...
We had a couple of sites where the NetTalk server would GPF and shut down from time to time, for no real explicable reason, and at no particular consistent point. One site especially would call up about twice a week with an issue. Both sites were not 'heavy' users of the portals we created - only the occasional updates.
To try and be proactive (and reduce embarrassment to us) I decided to implement a monitoring solution which would let me know when the sites went down so that I could (hopefully) reset them before the client realised. I used the wonderful, free, UpTimeRobot.com site for this.
The thing is - we've had UptimeRobot running for over two weeks now, and NONE of the sites have failed. At all.
I am not sure if the 5 minute polling that UptimeRobot does tends to keep the server 'alive' and precludes the condition that causes it to crash?
Like I said - long shot, but we've certainly noticed a big improvement in stability whilst our NetTalk servers in the field get a regular HTTP hit every 5 minutes.
I'm not shilling for UptimeRobot here. It is just the site we chose to use. I am assuming any other monitoring site/solution that does 5 minute pings might work too.
If you have a problematic site - try setting up a monitor with either UTR or some other one, and see if that improves it... Worth a shot...
Cheers,
Devan