Revit Architecture 2011 : Product is greyed out and cannot be selected for installation

Issue:
customer has clean uninstalled all autodesk products on this machine, customer attempts to install Revit Architecture suite 2011 and the product is greyed out and cannot be selected for installation.  Customer has also scrubbed the registry clean of anything autodesk remaining in the registry. Revo uninstaller does show that Autodesk Design Review 2010 is installed, however, attempting to uninstall this using REVO flags an error. As stated above all products have been cleanly removed.

System:
64 bit Win 7 Pro, 6GB RAM

Software:
Revit Architecture Suite 2011

Resolutions SO FAR (STILL RESEARCHING)
There are two things that can cause this issue.
Verify the Internet Explorer 7 (IE7) or higher is installed. Revit requires IE7 or higher to install.
The other issue is that if you have DWF Viewer installed. If you do have DWF viewer installed, uninstall it before installing Revit.
I would appreciate it if you would let me know if this answers your question. If it does not, please reply with more information about what you are trying to do so that I can provide a better answer.