Have you also installed the updated 10.10.1 ?
Open the logfile ( Console.app ) , launch a Time Machine backup and watch the entries in the logfile. What do they indicate ?
Search ( or filter ) for log entries that start with " com.apple.backupd " ( without the quotes )
I have a feeling there are problems that there are problems that the sparse bundle image file Time Machine uses to store backups on a network drive. Try the following:
1. Look on your Time Capsule and find the sparse bundle file Time Machine is using (probably has the name of your computer).
2. Double-click the sparse bundle to open it. Don't open it in Time Machine.
3. If what appears to be a new drive with the name of the sparse bundle appears on the desktop Launch Disk Utility, select that drive and verify. Repair the drive if necessary.
After this is complete close Disk Utility and eject the drive from the desktop. Now try running a backup and let us know the result.