If you are not already aware there’s an issue with the VirtualPathUtility object in the .Net framework. If you are trying to use the IsAbsolute or ToAbsolute methods with a path that contains a query string, you’ll get an exception thrown. A quick Google search on this issue will show you a ton of posts and ‘work arounds’ for this problem and I’ve implemented a custom work around for this in the ClientDependency framework as well. In fact, I only noticed this problem when testing the ClientDependency framework with .Net 3.5 and trying to register embedded resources through it (as see in this blog post here). Since I’d been developing the latest builds of ClientDependency in .Net 4, i had no problems at all but as soon as I changed the build to .Net 3.5, the exceptions began to show since web resource URLs have query strings.

So it the good new is that it appears as though Microsoft have finally fixed this bug in .Net 4! The bad news is that you’ll still have to use your ‘work arounds’ if you are targeting framework versions below 4.