Help me start .net!

Hi there!
I have win2k server and recently I have installed ASP.NET framework. But when I run a aspx page, I got the following error in IE.
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Server Application Unavailable
The web application you are attempting to access on this web
server is currently unavailable. Please hit the "Refresh" button in
your web browser to retry your request.
Administrator Note: An error message detailing the cause of this
specific request failure can be found in the system event log of
the web server. Please review this log entry to discover what
caused this error to occur.
--------------------------------

In the event viewer following errors are logged.

aspnet_wp.exe could not be started. HRESULT for the failure: 80004005

aspnet_wp.exe could not be launched because the username
and/or password supplied in the processModel section of the
config file are invalid.

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Can you please let me know where the 'config file' is located?
Also why my application is in't running? Please help me.