During a normal check, Time Machine detected that your backup file has become corrupted and is no longer useable. Backup files that include backups going back over a year or more are particularly susceptible to corruption. Appears to be a nature of beast situation with Time Machine and a Time Capsule.
On average, I see this message every 12-18 months or so on both of my Macs.
Click the Erase button to erase the current backup file and start over again with a new backup.
Your backups would be a lot more reliable if you connect a USB drive directly to your Mac and back up that way. I've gone for 5 years plus with no issues backing up this way.