AFP can be persnickety about you doing something as painfully silly as authenticating into a host using a password sent in cleartext (completely unencrypted). But when you’re troubleshooting it can be useful to disable this behavior, if only to test and then re-enable again. To do so:
defaults write com.Apple.AppleShareClient afp_cleartext_allow -bool YES
And to disable the warning:
defaults write com.Apple.AppleShareClient afp_cleartext_warn -bool NO
