In Windows XP, XP will give you that error but it's not about the administrator privilege but something about file or registry permissions.
Not to teach Windows admin here but even the admin must obey file and registry permissions. It's just sad that Microsoft elected to not cough up the right error.
By carlesness I did something that made my computer (windows xp pro, service pack 2 installed), to accept my name and password that have administrator rights, but then in users acounts don't appear who is the current user. My account aperar there, saying that I have administrative rights, but not as the current user. So I dont know who is the current user (or if it is possible to run with out one), but, as I can't use the administrative privilages, I can't try, to change setings there, when to make some change of settings they ask for some administrator name and password, mine is rejected.
So my question is what I need to be recognized again as an user with administrative rights (user acounts say that I have). thanks for your expertice, be indulgent with my negligence, and if posible help me as soon as posible.