Airport Time Capsule

Somehow your keychain entry for this password has gotten corrupted. I suggest that you use the Keychain Access app, locate your wireless password and delete it. You can just add it back again the next time you connect to your Wi-Fi network.

When you set a password on the TC and click to remember it.. that remember is on your computer in keychain.

Which password is being forgotten? Wireless password can be a bit messy and it is good to remove all the current wireless names.. delete them all.. reboot the computer and start over.. set your wireless to discover the wireless and save the password to your keychain.

If it does not work it could be cloud connection issue.