1. Send it (the file) to virus (at) avast (dot) com and inform it it a false positive.
  2. Add an exception into the AutoSandbox settings.
  3. Add an exception in the File Shield and on demand settings.
  4. Undo 2 and 3 after the virus lab correct this false positive.

By the way, send the file to www.virustotal.com and post back the link of the results.