I'm getting the same error (Unhandled Exception, System.UnauthorizedAccess to a path in /private/var/folders/<apparently random uuid>), running on macOS Sierra and mono version 220.127.116.11. Did you have any luck? Same here. macOS Sierra 10.12.5 (16F73), mono 18.104.22.168. Actually solved it by accessing the toolkit before clicking OK on the other window.