Test84:I think there are two solutions for your friend's problem. One could be that he doesn't have correct codecs for his videos.(most likely)
The other is that the video isn't in the correct drive.(for example:you have a c: and d: drive. Batch dpg/avisynth is in c: and the video file is in d:
(edit

Tell him to use K Lite Codec Pack. It's the best for batch dpg.