Identity of Backup has changed..umm, no it hasn't

I've been backing up for more than a year on my trusty Time Machine, sometimes there are hiccups but mostly it is seamless. This morning, "The identity of the backup disk has changed since the previous backup." Sorry, nothing has changed on my end. Nada. Nothing. Tells me "The disk may have been replaced or erased, or someone may be trying to trick your computer into backing up to the wrong disk."

So, I choose "Use this Disk" (other option was Don't Back Up). But it "fails."

What to do, what to do? Is some pirate out there trying to swoop in and steal my data?

Can someone help me get my head out of the oven?