Network connectivity between clients and servers may not work after the
installation of security update MS05-019 or Windows Server 2003 Service
Pack 1:
http://support.microsoft.com/default.aspx?scid=898060
To obtain this hotfix, it is a free call. [hotfixes are always free]
Call Microsoft, state you need KB 898060 and you'll get the hotfix.
--
An open letter to the Security Community::
http://msmvps.com/bradley/archive/2004/12/12/23540.aspx