Trouble adding users to local groups

Had a problem today with a Windows 2000 computer. We needed to add a user to the local Administrators group, and could not. Just clicking the "Add" button in the group membership window resulted in error message "An error occurred attempting to create the Object Picker. An error with no description has occurred." Luckily a solution was described here in Hidev, Inc. Knowledge base. In our case, the key HKLM\LDAP\Clsid was missing. Thanks!