Hello, I just did a fresh install of Rhino 5 and updated it to the latest service release. After that, when trying to install Grasshopper; I get the following error:
Don’t know if it’s the most recent, but it’s certainly recent enough to have a working installer.
You can just rename the .rhi file to .zip, open the archive and copy all the files to some place that makes sense to you, then drag+drop the GrasshopperPlugin.rhp into a running instance of Rhino to install it the old-fashioned way.