I'm having this problem. It started when I move the office, got broadband, and started up Revit. In my old office (no internet on the Revit computer) this never happened. I thought it might be related to getting my serial number kicked to 000-00000000, which is a known RAC2008 bug, but I no longer think that's the cause. It seems to be something to do with how Revit tells Windows about its license state.