Read the Knowledge Base -
How to: Convert to .AMV using the MP3 Player Utilities 3.68 from
here.
Step #6 tells you to put a tick in "Try another codec" if you get converting errors. Try that and let me know if that fixes the problem. If not, then I would try also updating the codecs you have on your computer too as it might be a fairly new codec that the Converter can't decode properly.