I’ve been using an 1TB WD external hard drive to transfer movies between 2 MacBook Pros for a long time, but suddenly I can’t write any files to it. If I do, it tells me the drive cannot be modified. I used it on another MBP and it worked with the help of Paragon NTFS for Mac. In this Mac, I have Paragon as well and I was able to write to the drive previously. Does this have something to do with my recent hard drive upgrade? I transferred most of the data after the upgrade.
I think your external hard drive is likely formatted in NTFS and the Paragon NTFS tool isn’t working on your Mac.
The solution is to use an NTFS for Mac tool that actually works. You can download iBoysoft NTFS for Mac to write to the WD external hard drive.