i would guess that you have a power issue, the unit uses more power with tvout active, and movie playing is one of the most power hungry things you can do.
So i would say that your ac adaptor is to weak.
ive had this problem with some videos when tried on the tv out (xvid hi bitrate mp3 audio), they were not reencoded to play on the 2x, its a strong possibility my batterys were rundown when i tried