GoPro .avi file not playing

[gopro-er]

Hi, I've just switched to SMPlayer from VLC, which was taking a looong time to load files.
SMPlayer is much quicker and seems much easier to use. I like it.

But...
I have some .avi files filmed on a GoPro camera and processed in the Gopro desktop app which aren't playing in SMPlayer. Actually they are playing as audio files rather than video. So I can hear them but not see them. They used to play fine in VLC...
I've tried searching this forum for help, but searches for things like '.avi' and 'gopro' don't return any results...

I'm using Win 7 Home 32bit
Anyone else got the problem? or even better, a solution?

Thanks.

[rvm]

Send the mplayer log (options -> view logs).

[gopro-er]

[rvm]