These are the "sids" numeric identifiers that the operating system uses to
keep track of users/groups. If the corresponding name is not displayed, then
either the user/group no longer exists or it is not being resolved for some
reason due to permissions or other problems. If this is a domain computer, I
would run netdiag on it looking for any failed tests that may help explain
why it is happening. The KB link below gives a possibilty as to why this can
happen if a domain computer does not have proper permissions in the Domain
Controller Security Policy. Keep in mind if you delete and then recreate
users or groups using the same exact name, a different sid is always
assigned to the new user/group. --- Steve
http://support.microsoft.com/default.aspx?scid=kb;en-us;262958
http://support.microsoft.com/default.aspx?scid=kb;en-us;321708