Problem With Xbmc Playing Videos

i've never had a problem with xbmc playing movies or videos before, but just recently for about a week its been acting all screwy.
all my videos i've already had on there work fine, its just the ones that i try to copy to my xbox now are messing up. they'll only play for about 5 seconds and then they'll exit on me, and its also strange that using the directional pad to fast forward/rewind doesn't work with these videos, but it still shows the video in good quality and the total time of the video too.
any help