Sansa Media Converter stops in mid download

oK I just got my Media Converter and its works for some videos and not others I have them all in the same format but it wont complete the download. For when I have the converter box up that gives you the % the top will say 100% and the bottom will just stay at 49% I have tryed it about 6 times. my mp3 is a e270 6gb and i have everything for it and it still dose it.