Hi Dale,

In IIS (under Win 2003), if you right click the Default Application pool and choose properties, then click the Health tab, you'll see an item for "Enable rapid-fail protection". By default this is checked and the number of failures is 5 and the time interval is 5 minutes. What this means is if 5 errors occur within 5 minute it will stop the application pool. This will result in the Server Application Unavailable message.

I would uncheck that and periodically review the event log for errors to avoid having the app pool turned off as a result of errors.

There are lots of scripts trolling sites trying to raise errors and if they manage to cause 5 errors within 5 minutes it can result in a denial of service because it turns off the app pool if rapid fail is enabled.

Hope it helps,

Joe