Not sure how far that you want to try to go with this, but I would not trust any hard drive that was 5-6 years old with my backups unless I had another backup plan already in place. That being said, here is what I would suggest:
Run First Aid on your Mac's hard drive to make sure that does not have any errors present that would interfere with Time Machine backups. To do that......
Open Disk Utility (Finder > Applications > Utilities > Disk Utility)
Click on the Mac's hard drive.....likely named Macintosh HD.....on the left panel
Click First Aid at the top of the window
It might take 15-60 minutes or more for the process to complete, depending on how much data is stored on the Time Capsule disk.
If you cannot part with the old backups stored on the Time Capsule hard drive, connect a USB drive to the Time Capsule's USB port and use the Archive function in AirPort Utility / Disks tab to copy the data over to the USB drive.
Then, erase the Time Capsule hard drive using the Zero Out Data option to completely erase the Time Capsule hard to wipe the drive clean to hopefully eliminate any disk errors, so you can start over with a new backup. The Zero Out Data erase might take 7-10 hours or more depending on the size of the Time Capsule hard drive.
Once the Time Capsule hard drive erase is complete, try to run a new backup of the Mac.
If you used the Archive function to copy the existing backups on the Time Capsule drive over to the USB drive, you might want to keep those backups around for a month or two in case you need to go back and pick up a file. Chances are, you won't need the old backups after a month or two and you can erase the USB drive and use it as a spare.
Unfortunately, there are no guarantees that erasing the Time Capsule drive and starting over will help to solve your problem. In other words, the only question here will likely be "when"........"not if".......you see the error message again.
If it were me, I would simply stop using the Time Capsule........(its time has passed)......and connect a USB drive directly to your Mac to back up using Time Machine. This method would be far more reliable than trying to back up to a Time Capsule.