Try a different converter.
Success! Viv la "Any Video Converter"! Very many thanks indeed Harm.
Glad that you got it sorted out.
Here's an ARTICLE with some background on AVI (also MPEG and MOV).
For playing your particular AVI (the Xvid one), you'll probably be able to play it in most players, if you download the DivX CODEC. That will still not let you edit it natively, in most cases, but at least WMP should be able to play it, along with DivX.
Thanks again. I do in fact already have the DivX codec, but will certainly read the article and if necessarry re-install.
I do in fact already have the DivX codec
Interesting. I am then surprised that WMP does not do a good job of playing. When I play an Xvid, the little DivX logo pops up in the Taskbar. Xvid is the open source version of DivX. I happen to have both installed, so maybe there is enough of a difference between the Xvid in your file and the DivX CODEC to be an issue. The Audio-only is one of the common problems with trying to edit these files natively. The other common problem is Video-only. Probably the MOST common is PrPro just flat refuses to Import it.
Good luck, and maybe add the Xvid CODEC, or better yet, use VLC Player (freeware), as it has its own CODEC set.