'Unavailable critical extension' returned when LDAP directory => W2K3 AD

[Tom]

On XP and Outlook 2003, Tools/E-mail Accounts LDAP directory pointing to a
W2K3 AD, after about 20 seconds, the error 'Unavailable critical extension'
is returned, however I can still use Advanced and can succesfully find the
desired recipients..

When using NT4, Window 98, and Winodws XP Address Book using the same LDAP
directory settings, the search is instantaneous and without the error

Any clues as to why and how to fix.. I have tried this with 2 different ADs'
with the same error.

thanks,
-tom