an attempt was made to load an assembly from a network location which would have caused the assembly to be sandboxed

I have also ran into this issue, but my problem occurred because the file had been blocked since it was downloaded from an unsecured source, GMail in my case. I solved it by

1. Right Click problematic file
2. Click Properties
3. Click Unblock

In my case it was the entire .zip file that was unsafe, so I unblocked the file before I unzipped it.

More on this solution here and here