As you have read in the Release Notes for ASP.Net MVC CodePlex Preview 5
the new release of MVC is not compatible with Service Pack 1 Beta. You must install SP1 (a long process) starting with a download from Microsoft.
The Preview 5 Release Notes say that you must install SP1 before you install ASP.Net MVC Preview 5, however, I found that installing SP1 on top of Preview 5 seems to work as well.
I am not certain that this is just the machines I was upgrading or all machines, but it did work for me.