This evening I came to installing MVC3 RC2 on both my desktop and laptop. The laptop installed first time, however I found that on my desktop it refused to install. Citing the following error in its install log: Installation failed with error code: (0x80070643)
After poking around in the log file I found that the VS10-KB2465236-x86.exe patch was where it was falling over. To try and get more information I found the temp directory with this file in and ran the installer manually. This also as expected errored, however this time when I looked in the log file I found a slightly different error: Install failed on product (Microsoft Visual Studio 2010 Express for Windows Phone - ENU)
The next obvious place for me to go next was to uninstall the Windows Phone Developer Tools, I figured I can always reinstall them. Upon removing this I then tried to install MVC3 RC2 again. This time it still failed, with the same error I had previously but this time for Visual Studio 2010.
As a final shot I wondered if the Visual Studio 2010 SP1 beta may have had the patch in and was causing some sort of a conflict. As such if I skipped the KB2465236 patch and simply installed the rest of MVC3 seeing if it would work OK.
It turns out I did manage to get it all installed, I had to grab the MSI Installers out of the temp directory that the main MVC installer creates and then run the installers in the following order: aspnetwebpages.msi, aspnetwebpagesvs2010tools.msi, aspnetmvc3.msi, aspnetmvc3vs2010tools.msi and finally nuget.msi
VS2010 now has the new templates and so far everything looks in order. This is a bit of a risky way of installing MVC3 RC2 but for me it works, if you have this issue and want to try bypassing the KB patch then I hope this has helped