Oracle 11i on Windows 2000 Pro -can't login

I installed Oracle 11i on Windows 2000 Pro. All is well except after the first login using Sysadmin/Sysadmin, it welcomes the System Administrator, but also says "Your session is no longer valid", and leaves it at a menu screen with no options but to login again.

It won't recognize the userid who is automatically logged on (says its an invalid login ID), even though it is part of the administrator and all Oracle security groups.

Bottom line... I can't sign on. Any help out there? I know I've seen this question posted before, but with no answer.

Thanks!

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