Files can’t be copied onto the backup disk because it appears to be “read only.”

WD External Drives External Drives for Mac
1

Time Machine tried to back up this afternoon and I got the above message.  The last backup was at 10:35 this morning with nothing of significance going on on my computer today except a little email and internet use (no, no strange sites visited…).  What has happened and how can I fix it?

2

What drive model are you using?

3

My Book for Mac

4

I’m sorry . . the 2 TB My Book for Mac.  Sorry I didn’t see your question last night and thanks for your help:)

5

Try opening time machine and check if there are back up created. Type time machine in spotlight and open app.