Running Rhino 5 & Rhino 6 on same Windows 7 PC - issues with Grasshopper

Hello, is it possible to run Grasshopper Plug-in on both Rhino 5 & Rhino 6? We have a user reporting issues when loading Grasshopper in Rhino5 (v0.9.0076) since he has had Rhino 6 installed. Maybe a version conflict for grasshopper? Error message reads “The CurveComponents Component Library was built against a different major version of the Grasshopper SDK: Local SDK = Referenced SDK = 6.3.18090.471”
any informatin or guidance would be most welcomed, thank you