If that doesn't work for you make sure you have the correct drivers. If you are trying to use the DX and not the D2 drivers you will also get this message.
The Correct drivers for the D2 (not the DX) are here , note this is from the US Linked site:
http://support.asus.com/download/download.aspx?model=Xonar%20D2/PM&SLanguage=en-us
good luck