First of all, great news that the ASP.NET MVC Release Candidate has finally been released. Full credit to the team for the hard work on this. You can get the download here However this is the first time I have had upgrade issues. Phil Haack has noted some of the issues here If like me you have lot's of CTP's and Add-Ins then you might experience some pain in Uninstalling MVC Beta on Vista SP1 This is the list of Add-Ins / CTP's I had to uninstall to get it to work Spec# PEX Resharper 4.1 Sourcelinks ANTS Profiler 4 Can't say I'm too impressed as it wasted over an hour of my time. As it turned out Spec# turned out to be the offending culprit, it's forgiveable to have issues with a third party product but a Microsoft one? Guess no-one on the ASP.NET team has Spec# installed.