Mac – Time Machine error – backup disk image could not be created

Since the verification process is akin to running fsck the filesystem check utility, this is the thing that will repair the backup or pronounce it dead.

If it fails too many times, you will then be left with a read-only Time Machine directory that you could clone somewhere else, restore the files you care, or wipe and start over.

Sadly, you are seeing all the progress that is normally available without running the tmdiagnose tool to collect detailed status and log when you ask Apple or a technician to help with time machine problems.

In most cases, I would say pick a time you can afford to be without backups (a day, a long weekend, a week) and set the Mac to not sleep and let it chug and see if it finishes. At the end of the period, you can decide to clone off the data to an attached USB drive just in case you need to retrieve something or just wipe the disk and start over.

Have you rebooted your Mac and run a filesystem check (or safe boot) to make sure your Mac doesn't have any directory damage?

Read only is a fail safe mode for the backups. It means there was a problem detected with the backup and you can only restore from it.

The system won't continue adding files since that would risk your losing even the ability to recover the files.

There is a procedure to re-attach a Mac to the existing backup once logic boards are replaced, but they assume that there isn't a failure of the backup at the same time.

You should have support from the people who replaced the logic board to help make sure you aren't just missing the steps to re-establish a backup, but if the backup were mine, I'd try backing up to a blank new USB drive and get a good backup now and then troubleshoot the Time Capsule to remedy the error causing the read-only status without risking your only backup. (Since the troubleshooting is to use Disk Utility to repair or erase the Time Capsule and then start over with an initial backup).