Lost ability to copy files from MacbookPro to WD external Hard drive

I havent copied files for a long time…the wd external drive is showing in my Finder…but how do I get files off my mac to my external drive.  I thought I could drag and drop, but this isnt working…any ideas please?

Hello,

Check out this link below.

How to copy or move files or folders to a different hard drive on a Mac 

If the drive is formatted for Windows then you have to format it for Mac before you can copy files to it on a Mac.

How to partition and format a WD drive on Windows (8, 7, Vista, XP) and Mac OSX

I’m having the exact same problem, and your solution did not help.  I connected my WD MyBook to my MacBook Pro, and unlocked the drive.  I can see the files, and I can even open the files.  

However, I can neither copy new files to the drive nor delete files that are currently on the drive.  When I try either of these actions, I receive an error message.  For example, when trying to delete a file, I get this message:

The item “xxx” can’t be moved to the Trash because it can’t be deleted.

Any advise about how to fix this problem??