This might be kind of a longshot, but if you hilight the "/Applications/Band-in-a-Box/RealTracks/Data/Style Demos Audio" folder in the Finder and do "Get Info..." on it, what are the permissions set to ?
I have had problems in the past with permissions on the audio folders preventing me from playing the audio.
I will include a screenshot of mine below, and you will note that I have given my account read/write access to the folder.
If you are willing to try, it is easy enough to add your account to the folder with read/write access, then click the gear icon and select "apply to enclosed items".
That has fixed similar problems for me in the past.
Hopefully this helps.
- Jay