Symptom
The Internet control panel (available when Classic is running) lists only one set named "Mac OS X". If you try to duplicate the set, or create a new one, an alert box with this message appears:
"Internet Config. Extension error -677 has occurred! Unable to continue."
The Internet control panel then quits without saving any changes.
Solution
The Mac OS X System Preferences application includes an Internet pane that allows you to make settings for accessing the Internet. The Internet control panel performs the same function. Settings made in System Preferences affect the behavior of Classic Internet applications.
Changes made to the Mac OS X set in the Internet control are effective for all of Mac OS X. However, you should use the Internet pane of System Preferences to change most settings. Some Internet control panel settings have no counterpart in the Internet pane of System Preferences, including those found in the News and Advanced tabs of the Internet control panel. You should use these tabs in the Internet control panel if necessary.