Can't able to Open .XcodeProject in OmniGraffle Application?

Actually I want to generate a Class Diagram of my existing Xcode Project. So i am using OmniGraffle Application. Here I tried with the Latest version of Xcode 6.0.1, Even I tried with Xcode Version 5.1. But I did not achieve. I am always getting this Alert Message, while opening my Xcode project into Omnigraffle.