It seems like it is not a failure in the action itself but rather a problem during with WiX runtime trying to load the custom action (e.g. referenced assemblies are missing).
The easiest way to test it is to have your custom action body completely empty (may be with only a session.Log("something")). If it works then it is a dependency problem and it will need to be fixed by defining the referenced assemblies (e.g.
The easiest way to test it is to have your custom action body completely empty (may be with only a session.Log("something")). If it works then it is a dependency problem and it will need to be fixed by defining the referenced assemblies (e.g.
project.DefaultRefAssemblies.Add). Unless of course it is some other dependency problem.