MPEGS Won't play - unsupported file

All of my MPEG’s, which I’ve been able to watch, are no longer playing.  I recieve an error that says ünable to play the selected format. 

Any ideas???

Reboot the box.

Thanks.  Worked.  2nd time this week it needed rebooted and I only used it twice this week.  Seem that last firmware update is a little buggy