We build our code to a central server and then use Powershell to install those build on our Development server. The upgrade to .NET 4 caused 2 problems with Powershell when we called
[Reflection.Assembly]::LoadFile()
First:
Powershell by default runs in .NET 2.0. When we tried to load our new 4.0 assemblies, we got this error:
Exception calling "LoadFile" with "1" argument(s): "Could not load file or assembly 'file://\\buildServer\Application\assembly.dll' or one of its dependencies. This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded."
At C:\Scripts\Deployment\Deploy.ps1:XX char:XX
+ $assembly = [Reflection.Assembly]::LoadFile <<<< ($file); + CategoryInfo : NotSpecified: (:) [], ParentContainsErrorRecordException + FullyQualifiedErrorId : DotNetMethodException
We need to tell Powershell to run in .NET 4.0 mode. To do that we need to create an app.config file for Powershell. In our case the file was created here: C:\WINDOWS\system32\windowspowershell\v1.0\powershell.exe.config, but YMMV based on Powershell's location. The new powershell.exe.config file looks like this:
<?xml version="1.0"?>
<configuration>
<startup useLegacyV2RuntimeActivationPolicy="true">
<supportedruntime version="v4.0.30319"/>
<supportedruntime version="v2.0.50727"/>
 </startup>
</configuration>
Now Powershell can run with both 2.0 and 4.0 assemblies.
Second:
The security features are a bit different when running 2.0 vs 4.0. This difference caused a problem when running assemblies from our Build server on our Development server:
Exception calling "LoadFile" with "1" argument(s): "An attempt was made to load an assembly from a network location which would have caused the assembly to be sandboxed in previous versions of the .NET Framework. This release of the .NET Framework does not enable CAS policy by default, so this load may be dangerous. If this load is not intended to sandbox the assembly, please enable the loadFromRemoteSources switch. See http://go.microsoft.com/fwlink/?LinkId=155569 for
more information."
At C:\Scripts\Deployment\Deploy.ps1:XX char:XX
+ $assembly = [Reflection.Assembly]::LoadFile <<<< ($file); + CategoryInfo : NotSpecified: (:) [], ParentContainsErrorRecordException + FullyQualifiedErrorId : DotNetMethodException
Now we simply add the loadFromRemoteSources switch to the powershell.exe.config file we just created so that the entire file looks like this:
<?xml version="1.0"?>
<configuration>
<startup useLegacyV2RuntimeActivationPolicy="true">
<supportedruntime version="v4.0.30319"/>
<supportedruntime version="v2.0.50727"/>
</startup>
<runtime>
<loadfromremotesources enabled="true"/>
</runtime>
</configuration>
Now we are successfully loading remote .NET 4.0 assemblies in Powershell. Hope this helps.