One person had a similar issue a few years ago: Cannot Create Directory on Install
I posted some suggestions in that thread, and they also reported that uninstalling Opus and rebooting then allowed the new installer to work.
If you do uninstall Opus, note that it will wipe your configuration. Before uninstalling it, run the old version and use Settings > Backup & Restore to create a config backup so that you can import it into the new version, assuming you want to keep your current config.