Running PowerShell on .NET 4.0

Attempting to use Add-Type to load a .NET assembly in PowerShell this afternoon, I got the following error:

This assembly is built by a runtime newer than the currently loaded runtime

By default, PowerShell runs using the v2.0 .NET runtime, and my assembly is built against .NET 4.0. To get this to work, we need to persuade PowerShell to run on .NET 4.0

The best way to do this is the second answer on this Stack Overflow question. In short, you add a PowerShell.exe.config file that loads .NET 4.0.

You can check that this has worked by looking at the $PSVersionTable.CLRVersion variable in PowerShell.