I have a game that runs on .NET, and it doesn’t even start until I had to go uninstall the Behavior Shield in the Add/Remove panel.
What is the 5.1.XXX as that is probably the most crucial bit ?
If it isn’t 5.1.874 then you should try the pre-release build that has resolved some of those issues, see http://forum.avast.com/index.php?topic=68927.0