Application failures can be caused by a number of coding problems, each of which you will want to investigate using the data collection and analysis techniques and tools available to you. Typical application failures include crashes, where the application unexpectedly terminates, and hangs, where the application becomes unresponsive as it, for example, enters an infinite loop or waits for an even that will never happen.
Tracking such problems can involve trial-and-error as you collect and analyze data in various ways. You may find your own way that works best. Try the following steps: