I vote for an application error. It should have handled such scenario. I know these once-in-while bugs that are very hard to reproduce during the testing but for sure its application error.

These are some questions from my side which you must ask urself or ur application developers - these might give u some more clues.

By the way, how do you start the service? Is there an automated process for that? What is the condition that it checks on the database? Is this condition being frequently changed from somewhere? How frequently do you query the database for this condition (an infinite loop?)

24 hours * 60 days = 5184000 seconds = 86400 mins...has this something to do with the application? Some variable reaching its limit..causing some exception...

I dont know - anything could be happening there...is hard to tell without the code or the application on the desktop. Just guessing. See if it helps. Good luck.