Submit the file to avast. (virus@avast.com). Email a password protected zip, or submit from the chest, no need to password protect it in a zip. In either case, include in the message body a brief note explaining why you think it is a false positive and the vps that detected it. If using a zip, also include the password.
Until the detection is corected you can add it to the excusion list.
For on demand
right click the "a" icon, select program settings, exclusions, use the add and browse features here.
For on access
Left click the "a" icon, select standard shield, customize button, advanced tab.