For some strange reason my RAC 2010 software started giving the the following warning when I started up my REVIT.
"revit rendering library not installed"
After some minor investigation I noticed that REVIT was looking for the librabry file named "assetlibrary_base.fbx' file in the wrong place.
So under the REVIT 'Options' > 'Rendering' tab "Render Appearance Library Location'
I reset the path from:
'C:\Program Files\Autodesk Revit Architecture 2010\Program\"
"C:\Program Files\Autodesk Revit Architecture 2010\Data\Rendering\assetlibrary_base.fbx'"
AND PROBLEM SOLVED !