ffserver problems

I'm really having problems with ffserver streaming to WMP10.

ffmpeg grabs video to a file fine, no problems at all.  When trying to
stream, media player just doesn't want to know.

It starts off buffering, then says it's playing, but with no media being
shown/heard.  Then it'll start buffering again but the buffer level drops
rather than rises.  Something like:
Buffering 92%
Buffering 74%
Buffering 36%
...

Interestingly, if I press "q" to stop the ffmpeg process, I get a single
frame in WMP10.  I've tried with Real also, with similar results.

This is with the latest CVS, all worked fine in 4.8.

Any ideas?

--
Pete Foster