USB permissions??

My portable hard drive works with every computer except my Mac. Permissions say I have access to read & write but that's not how its working?

Also just to test things out I attempted to change permissions and my Mac is saying I don't have permission to do it??

Brand new Mac. I just bought it and set it up and this is the problem I'm having. I'm the only person who's touched this thing and I've only created one profile. Mine. What gives??

Also just updated to newest iOS so that's not it either. Whats the point of this thing if I can't use USB with it??