Time Capsule issues with MacOS Sierra

Since I've installed MacOs Sierra (and now I've updated it with public release of 10.12.1) I cannot backup to mu Time Capsule's disk and this error always appear: "Error Keychain error -25299 occurred while creating a System Keychain entry for the username ..."

I've tried everything (soft, hard restoring and resetting my TC + deleting my Backup disk, I've changed names, passwords... and it did't solve this very annoying issue! My Time Capsule was working perfectly until the installation of the OS Sierra. What am I missing here?...