david,
Never heard of this before. What format was original file? AVI, MPEG etc. Which amvconvert tool are you using? If ver 4.00, uninstall, and install 3.68. Test. If that doesn't work, try:
1 converting a different file type and test.
2 leave mode switch at default (2 I believe)
3 tick 'use other codecs' box
Make sure all codecs are up to date 1st by downloading them here:
http://www.mympxplayer.com/dload.php...file&file_id=6
Post back results.
Good luck,
I.