If you're like me, when you see Release Notes, you think "I don't need to read any stinking Release Notes." But sometimes they're important! This Topic 2.1 is particularly so. If you don't do what it says, it'll seem like WPF is working OK, except any attempt to display bitmaps will raise a FileLoadException because incompatible WindowsCodecs*.dll files are still in your \WINDOWS\SYSTEM32 directory. Follow the directions, and if you've already installed the June CTP Runtime Components, SDK, and VS extensions, all that's necessary is to uninstall the RC. There's apparently no need to uninstall the SDK or VS extensions first.