i dunno about the mp4 (im guessin its something to do with quality), but you other comp mite be missing some other codecs that your main comp already has. tell us what exactly the nature of the error is and maybe we can help you figure it out.

Btw, in the future, make the thread title more relevant to the quesiton so ppl know what the thread is about. putting the name of the file doesn't really do anything.