Cannot fast forward or rewind certain AVI files?

I know sounds crazy . . . I have the WD TV LIVE connected to my network, and also have a usb drive attached to it. I am able to fast forward and rewind most AVI videos, however certain videos simply do not, i press the buttons on the remote and no indication on the left of the counter that it is in rewind or fast forward mode? Am I missing something here?

All of these are XVID encoded AVIs

I cant fast forward or rewind m4v files.  I hear  you can re-label them mp4 but havent tried it.  Even when it works the  fast forward is pretty slow.