You have deleted the application, but you still need to delete the content.
Please go to: Library/Application Support/Steinberg/Content/ Groove Agent/ VST Sound and delete the VST Sound folder.
If it still doesn’t work then delete the Groove Agent folder inside the content folder.
Thanks for the advice, but for the record, that didn’t work. With all due respect, the issue is not [SOLVED].
In order to get the message to go away, I had to experiment, and delete FCP_SMT_138_Groove_Agent.vstsound and FCP_SMT_144_GA_Presets.vstsound from the Library/Application Support/Steinberg/Content/VST Sound folder.
But now, when I launch one of the new Groove Agent SE kits, I get a new error message from GA SE’s file browser. If I attempt to reinstall the content from the Cubase 8 installer, I’ll get the error message+crash again.
Please, you’ve got to make it easier for people to remove demos. I don’t mean to be rude, but this is totally unacceptable.