I recently purchased a My Passport 2TB External Drive to use with my MacBook Pro for Time Machine backups. After setting-up the Passport Time machine backed-up to it successfully. Since then it has not been able to back-up as the Passport says that it is “Read Only” due to its use by Time Machine. I have checked the permissions for the drive to ensure that all access is read and write but that made no difference. Yesterday I used Disc Utility to erase all the information on the drive and started again. Time Machine performed a full back-up to the drive. I checked this morning and saw that the warning about it being “read only” has reappeared and Time Machine has been unable to perform a back-up to this disc. I am perplexed at where to look for the solution. When this MacBook was my main computer I always used an old 1TB My Passport external drive for Time Machine with no such problems.
Maybe you should try contacting WD’s Technical Support about this.
To Contact WD for Technical Support
The link below will allow you to call support.