Is this something new or has this happened before? Do you get the same message if you try formatting it on another computer?
Right click on the drive in Windows File Explorer and then click on the security tab. Once you have done that make sure that you have permission to write to the drive. Be sure to look for your username. If it is not in the list then you may need to add it and give yourself the permission you need to write to the drive.
If this is new and the drive has worked in the past it is possible that the drive is corrupt and went into read-only mode to protect the files from accidental deletion. If that is the case then salvage what you can and get a new drive.
Update: I unselected my answer as the "Best Answer" since your problem has not been resolved.