Well, I'm just facing the same Kind of Problem, but after installing the latest Windows updates it still doesn't work. I have a Dualboot System on my Laptop so i tried to run ArcGis Diagrammer on Windows 8.1 and 7 (both 64 Bit)without any success. Then I tried to run it on a Computer with 8.1 32 Bit and still the same Problem. Do you have any other suggestions maybe? I'm really thankful for any Kind of Support!