variables in main page used in chart

Thanks Ray
I tried the following but couldn't get it to work.

In my main page (we'll call it mypage.asp) I have the following code

<%
strPITagname = "opcLab-19"
Session("cTag")=strPITagname
%>

I then test that it contains a value on this page by the following code which displays the correct value opcLab-19

<%Response.Write(Session("cTag"))%>

Then in my mypage_data.asp I have the following

Tag=Session("cTag")

and then go on to use the Tag variable in my SELECT query. Problem is I don't believe that the session variable is being carried over to this page? ...I know that the select query works because if I replace

Tag=Session("cTag")
with
Tag="opcLab-19"
then the chart loads correctly.

Any ideas