Recently, I went to install the released Windows Phone SDK 7.1 for Mango and got a weird error while executing the installable vm_web.exe with a message box saying

Visual Studio setup cannot run in compatibility mode.
For more information see the ‘Installing’ section in the Visual Studio readme at

Bah, this was humbug and I had VS Ultimate installed with all the latest service packs.

A little snooping around gave me a very simple solution.
Simply, copy your vm_web.exe to C:\ and run it from there. This worked like a charm.

Props to the post:

How did that guy even think of this simple fix, I wonder?

Hope it helps you…