Video/Audio not working for the whole file

[mesoteto]

This is my first time every with a Mp4 player and it was nothing more then the ebay special (cant justify paying for an i pod)

1-it is an off brand with the title MP4 player on the front

2-it only plays AMV video files, and i am using the AMV converter 2.0 product

3--for some reason it will play the video file about halfway threw then the audio starts to skip /fast forward and will actually jump to the next file when it reaches the end

4-but it doesn't do this every time

5-the original file plays just fine as an rvmb file

any help would be great and nice site guys