I don't know ISAPI or IIS, so I cannot judge if this is relevant, but this guy http://blogs.msdn.com/david.wang/archive/2005/09/12/Question-about-GetServerVariable-QUERY-STRING.aspx gives some reasons why the server variables might not be filled out.

In reply to Re^3: Getting a query string. by gmargo
in thread Getting a query string. by Eagle_f91

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