Below are a collection of Instructions on how to synch your calendar with various programs.
Changing one password and not the other, means you have 2 passwords to access your email. You can use both passwords to access your Mail and Webmail (IMAP/POP3/SMTP/HTTP), however this wont work when used for Calendar or Pronto or Instant Messaging.(XIMSS/CALDAV)
Hopefully, this will get fixed in the next patch, in the mean time, you will need to use the Internal password to access Calendar, Instant Messaging and Pronto. If you forget the password, you can login using your current password to the web interface and change your internal password.