Loading .net 4.0 assemblies in PowerShell 2.0

This post is about changing the configuration of a managed application to load the correct .net framework.

.Net assemblies can be load using the command:

Add-Type -Path ./MyDotNetAssembly.dll

The last versions of Visual Studio build .net assemblies for .Net Framework version 4.0 or higher. By default, PowerShell uses the .Net Framework version 2.0 run-time, and then you get the following error message in PowerShell:

Add-Type : Could not load file or assembly 'file:///C:\...\MyDotNetAssembly.dll' or one of its dependencies. This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded. 
At line:1 char:13
+ Add-Type -Path .\MyDotNetAssembly.dll
+                ~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : WriteError: (:) [Add-Type], BadImageFormatException
    + FullyQualifiedErrorId : System.BadImageFormatException,Microsoft.PowerShell.Commands.AddTypeCommand

To resolve this problem you can change the config file of PowerShell to let it load the .Net Framework version 4.0 instead of version 2.0. This can be done using the PowerShell.exe.config file. Locate the program PowerShell.exe which is typically C:\windows\System32\WindowsPowerShell\v1.0, and create/update the file PowerShell.exe.config beside it, with this configuration:

<?xml version="1.0">
<configuration>
  <startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0.30319"/>
    <supportedRuntime version="v2.0.50727"/>
  </startup>
</configuration>

On 64-bit machines, the location of 64-bit of PowerShell is the same, but the 32-bit version of PowerShell is located under C:\windows\SysWOW64\WindowsPowerShell\v1.0. When you use the 32-bit version of PowerShell, you should create/change the config file there too.

The same trick can be applied to other software that hosts PowerShell, such as PowerShell_ISE.exe. All you need is create a application.exe.config configuration file beside application.exe.

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