Hi...
This probably has something to do with WildTangent.
What is the file in particular? Is it an executable file (.exe)? I have faced this before myself and if it's a game executable file, you will either have to create an exception in avast's main and real time scanners or lose the ability to play the game.
There are many who feel that WildTangent software includes spyware, which (at least) a few AV's, including avast, detect. Here is one article on the subject here...
http://www.pcmag.com/article2/0,2817,1601598,00.aspDepending upon how you feel about this issue will decide your course of action.
EDIT: Now that I reread your post, are you sure it was avast that informed you of this infection? What was the exact message? Is there a possibility that it could have been Windows Defender or a program like it?
Best Regards...