The reason this is happening is because buffering is turned on by default, and IIS 6 cannot handle the large response.
In Classic ASP, at the top of your page, after <%@Language="VBScript"%>
add:
<%Response.Buffer = False%>
In ASP.NET, you would add Buffer="False"
to your Page directive.
For example:
<%@Page Language="C#" Buffer="False"%>