External authentication

In Oracle8i (8.1.7.0.0) I created new user and defined that it's password should be externally authenticated by Windows 2000 Professional. The authentication prefix in init file is defined as blank string (""). Then I logon into Windows with the same username as previously defined in Oracle but Oracle does not want to pass me through. What's wrong?

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Stjepan Brbot <Stjepan.Brbot_at_ZG.HiNet.HR>