You try running a cleanup or open with an audit on the Revit file? Create a Navisworks view and suppress items that you don't need to pull in. Update navis import preferences to only pull in the Navisworks view, check to see if the preferences are pulling in linked cad files (Do you need them?) same with linked Revit files. Sounds like someone puled in a CAD link or CAD inserc and its messing with the import.
