I opened Super Duper this morning to do my usual incremental backup but SD opened with a different window. This one indicated that it would be doing a completely new backup including the need to choose a disk.

Shortly after, as Time Machine attempted to do its backup, a dialgogue box appeared with:

"The identity of the backup disk "Time Machine" has changed since the previous backup.

The disk may have been replaced or erased, or someone may be trying to trick your computer into backing up to the wrong disk."

....and I was presented with two radio buttons.

Use this Disk and Don't Back Up

I then opened Time Machine and it said....

"Latest backup to Time Machine October 7, 2017" .....which is definitely wrong. I've done file restoration in the last week.

And, if I open the file restoration now, I don't get any choice to do so.

So, long story short....I have two backup programs gone awry. The only change I've made in the last few days was the latest Apple Security update.

Edit: In addition to the above, my DropBox seems to have reverted to the equivalent of a brand new install. DropBox keeps searching for an account and, when it doesn't find mine, opens the "Sign In to Get Started" dialogue box.

Ideas?

Edit 2: Well, I'm mystified. Before taking my dog for a walk I did a shutdown. Upon our return and a rebooting, everything's back to normal.

I was also having some issues - although different ones - with HIGH SIERRA.

I did a CLEAN install - erased the hard drive - and reinstalled SIERRA. Then, recovered my stuff from Time Machine backups.

P.S. I will give HIGH SIERRA a few more weeks (months?) to see if the bugs get worked out with updates before upgrading (?) again.

"We're sorry for any inconvenience we may have caused, we needed to borrow the biological unit's arithmetic assistant for the day."

- The Aliens

It appears you did it again but, fortunately for you, all is once again back to normal following a Disk Warrior directory rebuild.

Try it again and I'll sic my dog on you.

- The Earthling