Failed time machine backup: volume not available anymore
This isn't definitive, but the first thing to check is whether your system can mount the Time Capsule drive at all. Eject the Time Capsule drive if mounted, reboot your system, reconnect it, and see if it shows up in Finder and Disk Utility.

If not, there's a disk mount problem. You need to figure that out first, because Time Machine will not run without a known disk target to write to.

If the disk does show up, then there's some issue with Time Machine. It could be corruption of your backups, or of your Time Machine binary, or something related.

Sorry this isn't definitive, but I'd recommend checking disk status first to isolate the problem.