Intranet Single Sign on error, the web go to internet

Hello,

I use C# to do a single sign on ( the file is login.aspx)

When client browse to server in the same intranet zone in IE, the status bar will show intranet if success, otherwise, it will show internet and page not found.

My server IIS setting :
IIS properties ,
HTTP Kepp-Alives Enabled checkbox ticked
Anonymous Access checkbox un-ticked

Client setting :

Internet Options - > Local intarnet - > Sites - > Advanced - > add my login.aspx url in it


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