Portable HDD write protected on one computer but not another?

Hi everyone,

So I have a 1TB portable HDD that I've used for years. Yesterday I moved it to another computer (we'll call it computer B), copied some files to it and reconnected it to the computer it lives to (computer A). Today I realized I was still missing a few files and reconnected it to computer B and the machine told me it was write protected. To my knowledge, I didn't change any settings so I'm at a loss to what happened. It still works just fine on computer A. I looked at the drive properties and nothing jumped out at me (All of the permissions looked correct) Any ideas on how to fix things or things to try??

Thanks in advance!

Edit: I figured it out, I used the diskdrill utility program to make the disk writable again (it had an option to do so).