Time capsule not backing up Since many days, my time capsule, isn't making any backups. I checked the light status and its green, when choosen the command for backup now, it spends good amount of time (10-15 min) saying "preparing backup" and then failing, and upong entering "Time Capsule" preferences and choosing the red icon, I am showed the following message 

I tried restarting time capsule and my mac. But nothing works, My system is updated too. How can i fix this problem and why is it happening?
It clearly advises you to use Disk Utility and repair your back up disk.