No idea why this limitation exists, but apparently it is not possible to call pinvoke methods in a nested class from a method in a generic class.
 I had something like this:
public class Foo
{
    private class FooGeneric
   {
        private HandleRef handle;
        private const uint SOMEMSG;       private void DoSomething()
       {
           NativeMethods.SendMessage(handle, SOMEMSG, IntPtr.Zero, IntPtr.Zero);
       }
       Â
        private static class NativeMethods
        {
           [DllImport(“user32.dll”, CharSet = CharSet.Auto)]
           public static extern IntPtr SendMessage(HandleRef hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
        }     Â
   }
}
Just before DoSomething was called in my code I got a TypeLoadException with the message:
Generic method or method in generic class is internal call, PInvoke, or is defined in a COM Import class.
Solved it by moving the NativeMethods class outside of the generic class.
