Time Machine is read-only message

Hi,

I recently started backing up my 300GB iMac hard drive to a Seagate external (over 300GB partition of a 2TB external). The iMac HD has about 45GB space left. Everything was going ok until yesterday, when I started getting a pop-up message with the TC logo, "Time Capsule is read-only. Designate an alternate destination" or words to that effect.

Does anyone know what this means? The external drive is larger than the iMac HD, so I don't see how it could be full...

Thanks,

Elihu58

Follow this troubleshooting from Apple: Time Machine: Troubleshooting backup issues

But I think it will involve using Disk Utility app and clicking "repair" on the external backup volume.

Thanks for your reply. I wound up getting Apple support on the phone and they directed me to do as you said. However, since "repair disk" was greyed out in the disk utility choices, we clicked on "verify disk" and that cleared up the problem.

Thanks!