Try moving your file to a different location such as your desktop. The message, as you have correctly understood, is telling you that the OS is not permitting changes to the file. You'll need to examine the permissions on all folders enclosing your file and you may find that the file itself has the "read only" property set.
Individual files can be set to "Read Only"
Get Properties (or Get Info) of the database - you don't say Win or Mac, I assume Win.
Also the location of the file can prevent changes - move a copy to your desktop.