Solved: Changing “ASP.NET Web Pages” installation fails after Visual Studio 2010 SP1 install.

It seems VS 2010 SP 1 modifies the framework paths in the registry to contain a trailing backslash, which causes the uninstaller for the old version of “Microsoft ASP.NET Web Pages” to fail.

Steps to workaround are:

1. Remove the trailing backslash from the following registry keys:

HKEY_LOCAL_MACHINESOFTWAREMicrosoftASP.NET4.0.30319.0Path

HKEY_LOCAL_MACHINESOFTWAREWow6432NodeMicrosoftASP.NET4.0.30319.0Path

2. Uninstalled the old version of “Microsoft ASP.NET Web Pages”.

3. Add the trailing backslash back to those keys.

4. Install MVC 3.

This tip from the ASP.NET forums just saved my day…