Today I've seen very strange and unpleasant error while trying to run some freshly created Silverlight application. It said: Code# 2103 Invalid or malformed application: Check manifest Fast search by popular search engines gave me this and this places, but everything mentioned there I've already knew or tried before... So what is it? Let's see what it was and how it was solved. Let's reproduce it. I'm creating new Silverlight 2 project, compiled it it works... My simplest project...