Hello, laffey_!
Thanks for using Apple Support Communities, it's great to have you here. We want to help you get this permissions issue sorted out so you can manage all of your external drives seamlessly.
The first thing that we recommend is that you make sure your Mac is running the latest version of macOS available. You can do that from System Preferences > Software Update. Updates introduce new features but they can also include bug fixes and enhancements that may resolve these types of issues. Once you're all up to date, go ahead and test the issue again and see if you have better luck.
If not (or if you're already up to date) then another good troubleshooting step is booting your Mac into Safe Mode and seeing if you're able to have read & write access there. Booting into Safe Mode can help isolate issues and give us some more information and oftentimes will resolve the issue in and of itself. Here's how to do that: Start up your Mac in safe mode - Apple Support
We hope this does the trick for you!
Cheers.