WPFFontCache_v0400.exe

caches font information for all WPF apps. WPF apps will work without it but apps will start faster and load fonts faster with it running.

1. Stop the 4.0 service
2) Go to \LocalService\Local Settings\Application Data\ and delete all of the WPFFontCache_v0400* files.
3) Start the 4.0 service again
4) Start VS and try to make it happen again