Packaged Project Crashes During Play

Hi All, My project plays fine in the editor but on packaging the project and playing for a while with a friend the project randomly crashes during play. The project is an online FPS multiplayer and I would like to try and understand whats causing it to crash. How would I go about finding what would cause this crash and is there any tuts that can help with this sort of thing; understanding and debugging packaged project crashes. It appears to say ‘call stack’ and then crashes back to windows.

Any help and advise will be greatly appreciated.

Cheers in advance