Get Types in assembly (error: System.Reflection.ReflectionTypeLoadException)

The error message says everything you need, really:

try {
    // your code
} catch (ReflectionTypeLoadException ex) {
    // now look at ex.LoaderExceptions - this is an Exception[], so:
    foreach(Exception inner in ex.LoaderExceptions) {
        // write details of "inner", in particular inner.Message
    }
}

If you use the Entity Framework, check if version in Web.Config is the same referenced in your project.