It sounds like it could be your permissions. You could try opening up your permissions and see if that helps and then you can adjust things from there.
If you go to Storage -> Volumes (on the sidebar / left side of GUI), then below the name of your volume you should see 'Change Permissions'.
Click on that and a window will popup and you'll see an area that says 'Mode:' select all of the checkboxs for Read/Write/Execute and for Owner/Group/Other.
Then click on the checkbox at the bottom that says 'Set Permission Recursively'
Then click on the 'Change' button
You might have to wait a few minutes if you have a lot of files, but after that give your Xbox another try.
Hope that helps, if not report back and we'll see if there's something else.
I don't have an Xbox, so I'm just trying to give you some general pointers.