ASP.NET 1.1：

打开 C:WINDOWSMicrosoft.NETFrameworkv1.1.4322CONFIGmachine.config

设置：
< location allowOverride="false">

< identity impersonate="true" userName="" password=""/>

ASP.NET 2.0 以上：
C:WINDOWSMicrosoft.NETFrameworkv2.0.50727CONFIGweb.config

设置：
< identity impersonate="true"/>

如果没有此两项，分别进行增加：

< location allowOverride="true">  改为：< location allowOverride="false">
        < system.web>
            < securityPolicy>
                < trustLevel name="Full" policyFile="internal"/>
                < trustLevel name="High" policyFile="web_hightrust.config"/>
                < trustLevel name="Medium" policyFile="web_mediumtrust.config"/>
                < trustLevel name="Low" policyFile="web_lowtrust.config"/>
                < trustLevel name="Minimal" policyFile="web_minimaltrust.config"/>
            < /securityPolicy>
        < trust level="Full" originUrl=""/>
        < identity impersonate="true"/>  < !--  这里增加 -->
        < /system.web>
    < /location>