This most often means that your application has thrown an unhandled exception, which very often results in behaviour like this. Getting more information on that exception would be the task you are facing.
I assume you mean this occurs on a life production server, in which case low level debugging sessions are probably out of the question.
In many cases, you can install an exception handler, catch the error and log it. In other cases, you may be able to attach to the worker process, using Visual Studio for example, and catch the error there. See more on your options on our Exception handling article here.
Hope this helps,