The keychain can cause problems if the login keychain password and the users password get out of sync. This can happen by error in one of our images or sometimes when resetting a user password. The user will complain that they keep getting a dialog about the keychain pop up - usually in Safari.
The solution is to delete the “login” keychain. This is easily done using the “Keychain Access” utility found in /Applications/Utilities. While logged in as the user run the application.
Go to the “File” menu and select 'Delete keychain “login”'. In 10.5 you may have to select the “login” keychain first. Now log the user out and log back in again and the Mac will create a new login keychain with no password sync problems.