Time Capsule backup fails. Reports disk not in correct format.

Unfortunately, the hard drive is right on the verge of failing to operate at all. Since the drive cannot be repaired, the Time Capsule will need to be replaced.

Hopefully, the Time Capsule is still covered by the warranty, so that Apple can replace the device for you at no charge. If you have AppleCare in effect on any of your Macs, the Time Capsule will be covered, even if it is out of the normal warranty period.

Take the Time Capsule to an Apple Store....if you have one near you.....or contact Apple Support directly to get the process going. Good luck.

http://www.apple.com/support/contact/

I hope that I am wrong as well, but I've seen the same type of error on a Time Capsule that I had here, and while it worked for awhile longer when I started seeing the error reports, the drive failed outright after a few more weeks.

Then, when I opened Time Machine I found only one previous backup. I have been backing up to this 3TB Time Capsule for at least a year. Why would it suddenly think the disk is in the wrong format and why would I only see one previous backup?

The Time Capsule would not have deleted all the previous backups and started over again unless it detected a disk problem. If it deleted your backups and started over again once, then I'm afraid that it will do it again. That was my experience. After a week or two of "new" backups, I got the same error message again, and the backups were again deleted. I tried again, but after a few days, the disk just failed outright, and backups were not possible after that.

But again, I hope that yours will be different.

If the Time Capsule drive does fail....and you have no warranty on the Time Capsule.....then you don't need to make a 4 hour drive, since Apple will tell you that there is nothing that they can do for you other than sell you a new Time Capsule.

Time Capsule was purchased April 2014. Unfortunately, I didn't get AppleCare on it

I don't think that you understand what I mentioned earlier about AppleCare.

AppleCare covers your Mac.....but any other devices like a Time Capsule, AirPort Extreme, AppleTV, etc are also covered as long as they are no older than 3 years.

So, if any of your Macs are covered now with AppleCare, that coverage will extend to the Time Capsule, and you will get a free replacement Time Capsule from Apple.

I ran Disk Utility Verify Disk on the Time Machine backup drive. I reported that the drive needed to be repaired. The repair failed.

That is what I was afraid of. At least you won't spend another few weeks backing up to the Time Capsule only to have the backups deleted again.

only a year and a half is pretty crappy for a rotational drive.

I agree. But since Apple does not make hard drives, you cannot really blame them for a drive failure on a product that was made by Hitachi, Samsung, etc. The drive on my Mac laptop failed after only about 9 months. Since the drive was made by Seagate, they get the blame on that one.

One of the 3, 3TB time machines that I have, indicated a disk failure today. I told it to zero the drive, which it says will take overnight to do. I'll check tomorrow morning to see how it fared, but I think I will take mine to the Apple store to get it repaired/replaced. It would be best to do that yourself, as Bob says. I would call Apple and see if they can assist you on the best choice of resolution given your distance from a store.