Superku are you sure that your model has the same skin mapping as mine (see screenshot)? All vertex that occure only 1 time in the uv mapping also work for me (you only try 1 vertex so maybe you had luck).
Could you upload the model if the error still doesn't occur for you? Thanks

Btw. if I want to create a mesh that has seperated sides like in the skin mapping screenshot, how would I have to do that? I see no other way than creating the same vertex more than once (because one vertex can't have different uv coordinates)?