You must update all the Web servers that are running Windows SharePoint Services in a Web farm

You must update all the Web servers that are running Windows SharePoint Services in a Web farm, and you say SP2... and more here. How to configure a Windows SharePoint Services virtual server to use Kerberos authentication and how to switch from Kerberos authentication back to NTLM authentication.
You receive a "The Windows SharePoint Services virtual server has not been configured for use with ASP.NET 2.0.xxxxx.0" error message when you connect to the home page of a Windows SharePoint Services Web site (bad day for you).
You need to read : Guide for installing, configuring, managing, and maintaining Windows SharePoint Services. Or this one on-line.

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