The web-installer for VS2012 Pro gives me the error that it's beeing run under compatibility-mode (even though it's not). I copied this from the log-file:
Stop Block: CompatibilityMode : Windows Program Compatibility mode is on. Turn it off and then try Setup again.
I made sure in every way I know of (even going into the registry and deleting the node for the install-file in the compatibility-settings) that it was in fact not running in compatibility mode, then I tried to run it in compatibility mode. No matter what I did I got the same error.
The standard installer (not web-installer) seems to work though.