You can add the file name/path to the exclution list in the standard shield. Since you have been playing this game for some time, it is in all likelyhood a false positive.
Please send a passworded zipped sample to
virus@avast.com , include the password and why you believe it to be a fp. Include also which program version and vps detected it. Check the file after a vps update to see if avast has included it in the update.
You can also check the file at virustotal
http://www.virustotal.com/xhtml/index_en.html . It's muti av online scanner.
Never delete a file that avast has detected. If you delete you have no options left because avast does just that, it deletes completely. Chose send to the chest instead. The file is safe there and you can investigate. If it is a fp you can restore the file, or if it is truly infected you can delete it from there. Lucky you have the cd for the game.
Welcome to the forum