Backups via Time Machine to our 2TB Time Capsule have not gone smoothly the last several months, with the backup always stopping with an unexplained error.
After reviewing this 2010 page from Joe Kissell on troubleshooting Time Capsule problems, I tried Disk Utility and then finally opted for a complete erase of the drive and a fresh Time Machine backup. The dialog UI has changed, of course, and it took a bit of spelunking to find the Erase command in the Airport Utility.
The fresh backup copying seems to be going OK so far, and I'm hoping this brings an end to these intermittent failures.
Update, 2018-01-01: This did not help; still getting the error. May try another erase and then a hard reset of the Time Capsule. More later.