Eddie,
The Idle Time-Out setting is a very likely reason that your app pool would be shutting down. This setting specifies the amount of time the app pool should stay active after the last user request was processed. Under the default setting, the app pool was shutting down about 20 minutes after your last session.
As Derek indicated, if your app pool shuts down, all of SmarterTrack's background processes will stop. Setting your Idle Time-Out to 0 will likely keep your app pool from shutting down. It is also possible that your app pool could be getting shut down some other way, but the only way to determine that would be to review the event logs on the server for the time that the app pool was terminated.
If you continue to have issues, you may want to consider opening a support ticket to get some targeted assistance.
Andrew Barker
Software Developer
SmarterTools Inc.
www.smartertools.com