Error 2896 using a WiX C#/.NET 4 custom action

As a corollary to KnightsArmy's answer this error is also thrown when the DllEntry attribute on the CustomAction element is wrong. In my case I had a typo and the only error information I could get out of the log was the infamous error 2896.

I figured it out by running my msi with the /lvx option to get a verbose logging. I also had to move my action to the InstallExecuteSequence section to get a meaningful error message. When the call to the CA was in the PushButton nothing meaningful was returned.

<InstallExecuteSequence>
    <Custom Action='CustomActionTest' After='InstallFinalize' />
</InstallExecuteSequence>

System.BadImageFormatException: Could not load file or assembly 'JudgeEdition' or one of its dependencies. This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded.

I changed the useLegacyV2RuntimeActivationPolicy attribute to true. Everything started working nicely.

<configuration>
    <startup useLegacyV2RuntimeActivationPolicy="true">
        <supportedRuntime version="v4.0" />
    </startup>
</configuration>

These links helped get me up to speed:

• What does 'useLegacyV2RuntimeActivationPolicy' do in the .NET 4 config?
• http://www.marklio.com/marklio/PermaLink,guid,ecc34c3c-be44-4422-86b7-900900e451f9.aspx