Problems playing the videos

when i play the videos, some vidz plays normally but when i play two particular videos, which encounters problem. see the problem is that it starts playing normally, but after a few seconds the audio shuts off and in a few seconds the video stops playing and ipod return to video selection menu. these videos plays well in the itunes library on my computer....
i've converted all the videos in the same manner, by same converter at same bitrate....
can anybody tell me why is it happening???
can it be because i dropped my iPod recently????