Hello @cgrammens I downloaded and tested the latest Vray (hotfix4) for Revit and confirmed the issue. The problem is the Xceed.Wpf.Toolkit.dll conflict between Rhino and Vray. Go to the VRay install directory please (C:\Program Files\Chaos Group\V-Ray\V-Ray for Revit) and rename Xceed.Wpf.Toolkit.dll to Xceed.Wpf.Toolkit.dll.bak
Then load Revit again and RIR should load graciously 
