Recently I change the main password in Ubuntu. After restart it was I faced a new password dialog: "Enter password to unlock your login keyring". Searching the Internet after this issue, I found here a very nice step by step guide of how to get rid of this dialog.
For those of you that want the short version here are the steps to follow:
1. Ubuntu main menu -> Applications -> Accessories -> Passwords and Encryption Keys.
2. In Passwords tab, right click Passwords: login. In the menu select Change Password… option.
3. Enter your old login password and new login passwords. New password should be the main password from Ubuntu.