Visual Studio 11 - Design view is unavailable for x64 and ARM target platforms because the document contains custom elements

I'm test-driving Visual Studio 11 beta and it appears I've hit a major snag.

Has anyone tried opening an actual production WPF project that contains WPF windows with User Controls? When I try to open a WPF Window or control that contains user controls, the design view displays a nice error message:

"Design view is unavailable for x64 and ARM target platforms because the document contains custom elements."

It appears to be a major wtf... since most developer machines these days are x64.

* UPDATE: *

Reproduced this in a new VS 2011 WPF project:

1. Add a xaml resourec file with styles (in the same project as the user control)
2. Reference this file in a user control using the tag

Immediately, the "Design view is unavailable for x64 and ARM target platforms..." pops up.

As soon as I remove the resource reference, the designer starts working again.