private readonly string JAVASCRIPT_STARTTAG= "<script
language='javascript'>";
       private readonly string JAVASCRIPT_ENDTAG = "</script>";

   public static void NewWindow ( Page p , string url)
{

           string uuid  = System.Guid.NewGuid().ToString();
           //'uuid ensures uniqueness, the replace gets rid of non
html/javascript friendly values
           uuid = uuid.Replace("-", "").Replace("{", "").Replace("}", "");
           p.RegisterClientScriptBlock(uuid, JAVASCRIPT_STARTTAG + "var win
=
window.open('"+url+"',null,'height =300 width=420 scrollbars=yes');"+
JAVASCRIPT_ENDTAG)

}

You can try the Page..RegisterClientScriptBlock method instead.  I don't
know if it will fix your issue or not, just giving a suggestion.

Above is a static method I have to pop a new window.. .from a code behind
method.

Another hint ... is the domain issue.  Try passing in the FULL QUALIFIED url
.. as it will be on the hosting server.

instead of
string url = "ResponseCountReport.aspx";

try

string url = "http://www.myhost.com/myapp/ResponseCountReport.aspx";

just as a test to see if thats the issue.

you might experiment with the ~ thing also.