Scripts fail randomly in different spot.

Hi,

  I am just wondering why sometime my scripts fail in the middle of the test sometime it pass through the whole scripts with exactly the same scripts 6 hours run. The funny thing is, it fails in the different spot every time the scripts stop. I found out most of the problem is about timing issue and Keys method. I try to avoid some of the timing issue problem by using Wait method. I even need to repeat the 'Keys' method for the one it fails for the first time. The thing is I needs to scripts more tests instead of fixing the issue that occurs randomly in the existing scripts. Is anyone encounters this problem before? Hope anyone can help me out here. Thank you very much