I have a problem getting spdif passthrough with my 4850gs, previously was using 3870 without a problem

I'm connecting the card with hdmi cable through a dvi-hdmi adapter from the 3870 card to my receiver, using windows xp sp3. Using KM player + ac3filter with spdif passthrough ticked but the receiver does not receive ac3 or dts signal from the card, however it does receive a stereo pcm signal only The message log from kmplayer is saying that spdif output is disabled.

Does anyone uses the 4850 in a HTPC? Thanks.