...Still fiddling with one of these!!! I was trying to download a few YouTube clips, so I could work on different re-format options, to try to beat the dreaded 'file format error'.....I chanced upon the site :-
YouTube Downloader - Software to download and convert YouTube video
Apart from a video clip downloader, it also has a format convert utility.... I tried it, and,.. lo and behold!!! selecting the 'convert to' option to 'XVID MPEG-4 CODEC (AVI)' , everything I have tried has converted, and played successfully!!! the new files are about half the origional filesize, as well, if converted on the 'optimum' setting.......
Hope that helps someone.....
Cheers Fred