Hi, got a problem thats just occured with the web.config but not sure why. can anyone help?

I havn't changed anything:

Server Error in '/' Application.
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Configuration Error
Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.

Parser Error Message: The value of the property 'mode' cannot be parsed. The error is: The enumeration value must be one of the following: None, Windows, Passport, Forms.

Source Error:


Line 51: ASP.NET to identify an incoming user.
Line 52: -->
Line 53: <authentication mode="windows"/>
Line 54:
Line 55: <!--


Source File: C:\DHCD\www\web.config Line: 53


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Version Information: Microsoft .NET Framework Version:2.0.50727.3082; ASP.NET Version:2.0.50727.3082