Failed time machine backup: volume not available anymore How do I remount my existing backup without loosing the data on the existing backup and why did this happen? 

I have a macbook that makes time machine backups to a time capsule. 

Now time machine complains that it can't mount the backup volume and do a backup. I checked in finder and still see the network drive mounted for time machine backups in finder. Earlier I changed the admin password for the time capsule, but this shouldn't influence the backup right?

When I go to console.app I get following messages from the backupd service

com.apple.backupd: Starting manual backup
com.apple.backupd: Attempting to mount network destination URL: afp://Short%20TimeCapsule%20Name;AUTH=SRP@Long-Time-Capusle-Name.local/Data
com.apple.backupd: NAConnectToServerSync failed with error: 80 for url: afp://Short%20TimeCapsule%20Name;AUTH=SRP@Long-Time-Capusle-Name.local/Data
com.apple.backupd: Backup failed with error: 19
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.