Password error when changing user role

My site is running Drupal 4.6.3. I receive a "The specified passwords do not match" error when attempting to change the role of authenticated users.
I am logged in as the administrator (user 1) and I am simply trying to promote certain authenticated users to a higher level of site access. I would think that this can be done without knowing the user's password.
I am attempting this operation by using the following path: Administer/Users/List/User name/Edit/Account settings, then selecting the desired roles and clicking Submit. I invariably receive the "...passwords do not match" error.
Am I doing something wrong, or is this a bug?
Thx.