Time Machine

We will assume that you have a Time Capsule that your Mac(s) are backing up to using the Time Machine application......would that be correct?

Do you want to erase all of the data on Time Capsule hard drive.......

or

Do you want to only erase the backups that have been made by one Mac.....and keep other backups that might have been made by other Macs intact?

Not sure what you mean when you say that you cannot "busker" the last backup. (Maybe we don't understand the word "busker".)

Right-click on Peter Hayden's iMac.backupbundle

Choose Get Info

make sure “Locked” is deselected, and then check the Sharing & Permissions section. When you are sure the items are unlocked and not designated as Read Only or No Access, try again.

This is what things look like on my Mac:

Unfortunately, you do have the Catalina operating system running on your Mac. Catalina has wrecked Time Machine for a number of users.....including me.

My advice would be to copy the data that you want to keep from "Data" on the Time Capsule to another hard drive, and then perform a complete Erase on Data using the Zero Out Option in AirPort Utility. Then, start over with backups of each Mac.

There is no guarantee that that this will help, but it is about the only thing left to do at this point.

You might want to wait before you erase the Time Capsule disk, as another user might see this post and be able to help.

On your Mac......

Click on the Finder icon on the dock (the one with the smiley face)

On the left panel of the Finder window that appears look for the Locations heading. Older Macs might read Devices

Click on the name of the Time Capsule under the Locations heading and a folder named "Data" will appear to to the right......unless you have changed the name of the hard drive. You may be asked for the Time Capsule administrator password

Double-Click on Data and wait for the next window to open

Click on the name of the Mac whose backups that you want to delete to select the file

Click the gear icon at the top of the window and then click Move to Trash

There is no going back at this point, so make sure that you have selected the correct item to delete before you confirm. The deletion process might take 5-10 minutes or so on average.

When the process has completed, you can start a new backup of the Mac, which will take a long time. If you are using WiFi to back up, try to locate the Mac close to the Time Capsule to speed the process.

And what happened when you......

For each item, choose File > Get Info, make sure “Locked” is deselected, and then check the Sharing & Permissions section. When you are sure the items are unlocked and not designated as Read Only or No Access, try again.

Hopefully, your Mac is not running the Catalina operating system......which has plenty of file permissions issues with Time Machine backups.

Is it possible that you enabled the option to "encrypt" the backups when you first set up backups for this Mac? If you did, you will normally be asked for the password that you set up for this at the time.

Nice work!

I started getting that same error message after the last update to 10.15.5. Haven't tried to fix yet. Otherwise I have three years worth of bi-monthly updates after deleting the ones in between.