After upgradering to Mavericks, I have been bombarded repeatedly with the following prompt:
Messages agent wants to use your confidential information stored in “” in your keychain [Allow] [Always allow] [Deny]
No matter how many times each option is used, the popup appears again after a very short while (usually less than 15 seconds).
Erasing the Messages.app/iChat-related preference files from
~/Library/Preferences/ did not work.