I have exactly the same version as you. I have also B4J on my machine (v1.50) and it is running fine.
I'm currently updating a lot of DLL with Microsoft Update. Maybe that will solve the issue.
The problem is between Sandboxie, the program that I use to run apps in a sandbox, and .NET 4. As Sandboxie is used to run various versions of B4A on the same PC, I have some choices to make for the future.