Dear Albert,
Please address your question to all, not just to me personally.
I hope that other people will answer as well.
It is not mandatory to sign your DLL. For more information on that, please read the thread on code signing:
http://forums.autodesk.com/t5/revit-api/code-signing-of-revit-addins/m-p/5981560
You know that the obfuscator renames all your classes, methods and properties, don't you?
Well, it looks to me as if the obfuscator renamed your main external application class as well.
Therefore, no class named 'App' exists anymore.
Therefore, it cannot be found.
It no longer exists.
You can probably provide a list of classes and methods that the obfuscator should leave untouched.
Maybe you should read more aboout the basics (and dangers) of obfuscating before proceeding any further.
Cheers,
Jeremy