So, first I did a back-up using SuperDuper! I use a different partition for that. Then I queried the Internet, which, as we know, knows everything. I found the solution.
Apparently, Time Machine was interrupted during the last time it was run. Now, a power outtage can do that, and we had one today. But, this was user error. I turned my machine off last night when going to bed. And I did not check to see if it was running. It was a simple fix. I found it, via a search for the error message, at the MacCast Forum. The answer, from forum user "karinlord," was:
If Time Machine gets disrupted for any reason during a backup (e.g., hard drive unplugged, power failure) it seems to get stuck. Occasionally it gets stuck for reasons only known to Leopard. It's a known bug on the Apple discussion boards. What has worked for me is the following:
- ensure hard drive is powered on and connected to computer
- turn off time machine
- go to your backup volume, backups.backupd, "your computer name", and then select and trash "In Progress" or "Latest" (it will be the last one in your backup folder listing)
- turn Time Machine back on
- either wait for the next backup cycle, or what I do to be sure things are working right: force an immediate backup (control-click on TimeMachine, select "backup now").
This worked for me.