Strange sound problem!

[pal]

First of all I've got to say, I'm loving MediaPortal. I moved over when my xbox and XBMC could no longer take the files I wanted to throw at it.

I do have one small problem with it though and for the life of me I cannot work out what it going on. I have a Fatal1ty F-I90HD motherboard and am using both onboard graphics and sound via the HDMI port. It all works brilliantly until I leave MediaPortal in the menus for more than five minutes and then for some reason I am left with no sound when I try come back to it and try to play anything! If I come out of MediaPortal and go into media classic or VLC, both have sound. The only way I can then restore audio in MediaPortal is to reboot. The only way around it I have found so far is to start playing a film and then I can pause it for as long as I want as this seems to keep the audio running. Anyone got any ideas?

Thanks very much