exported game has white screen and crash error apears?

i have built my game and it runs perfectly on my pc, i sent it to my friends and they can get it working too in general but one friend is experiencing a problem, when he loads the exe file it opens a window but it appears white and then shortly after an error messge comes up saying 'the game crashed the crash report has been created (name of file and location) it would be great if you sent it to the developer' i tryed helping him online via skype etc. to get it working for him and he seemed to have all the files etc. we tried re downloading and checking all his essential software, java, java x64, flash etc. was upto date. everything seemed to be fine. i looked at a copy of the crash file and his system specs seem to be fine and no bugs were highlighted. what could be wrong? and how can i fix this?