I just ran across a problem on workstations with Internet Explorer 8 and Revit Architecture 2009. After an update to WSE 3 SP3 (Web Service Enhancements) was applied during the installation of another application and impacts Internet Explorer 8, Revit Architecture would crash when you try to start a new project with a template or open an existing project. This would result in a fatal error.
Autodesk support could not narrow down which Interner Explorer 8 component was causing the problem, but uninstall IE 8 and going back to IE 7 allowed RAC 2009 to function. None of the workstations with the error have RAC 2010 installed, so I am not aware if this impacts RAC 2010.