GH under .NET Framework not loading in Rhino8: GH_Canvas exception

Hi,
my Rhino doesn´t load GH any more in Rhino8, NetFramework runtime. It starts under .NETCore though.
I completely deinstalled and reinstalled Rhino, deleteted all plugins I could find, but this error persists.
Any suggestions?

Below is the error message I get.

Thank you,
Torsten

Command: Grasshopper
Error occurred loading plug-in
Details:
The type initializer for ‘Grasshopper.GUI.Canvas.GH_Canvas’ threw an exception.


Grasshopper

====
at Grasshopper.Plugin.GH_PluginUtil.LoadGrasshopper(String& message)
at GrasshopperPlugin.GrasshopperPlugin.OnLoad(String& errorMessage)
at Rhino.PlugIns.PlugIn.InternalOnLoad(Int32 pluginSerialNumber)

Unknown command: Grasshopper
Command: _Options
Error occurred loading plug-in
Details:
The type initializer for ‘Grasshopper.GUI.Canvas.GH_Canvas’ threw an exception.


Grasshopper

====