I develop application with ASP.NET and C#. I generate signature with OAuth.cs from http://www.oauth.net/. I get always error: signature_invalid. When I check signature with your demo application, she is different. 

How do I generate signature with OAuth.cs? It is possible? Could you public c# code your demo application for generating signature?

PS: sorry for my bad English 

 I'm not sure about the toolkit you are speaking of, and without seeing your oauth.cs code I couldn't really tell you what is going wrong.  I use the following toolkit and have been successful: http://www.codeplex.com/myspacetoolkit.

The examples have an incorrect resource uri, just change it to the correct one and you should be fine.