Hello!
The new Avast! has a problem working with Sandboxie. The old version, 4.8 had no problems. Here’s more about it: http://forum.avast.com/index.php?topic=58225.0
I hope that you can find out what’s wrong and repair it. Thank you. 
indeed, context menu scanning isn’t working… have you noticed any other conflicts?
No, but I haven’t tried to scan a sandbox from Avast!'s GUI, so I don’t know… I still have the 4.8 installed at the time.
Will you fix this?