popcap / Win32:Adware-gen ?

My wife and I both enjoy playing MSN Games...particularly Zuma ... and on my laptop, this is no problem. About 2 weeks ago, though, AVAST pops up a malware warning when we try to play on the desktop. It tells us we are infected with Win32:Adware-gen ... and to move it to the chest. So we do. I run Ad-Aware, and it picks it up, I delete it. I downloaded SpyBot today, it didn't even see it. After doing these things, I go back to MSN games - to a game I've played on this computer (desktop) 100 times ... and Avast captures it again and keeps me from playing. I'm pretty confident that this is not a big deal ... but how do I get around this ... solve this? I looked through the archives and didn't see anything in the subject lines on this subject. Popcap is the maker of the game.

big poppa