Keep Session Alive!!
When a new window is being opened from a modal or modaless form, it may loses the session. The cause according to Microsoft "This behavior occurs because Internet Explorer windows that are opened from a from a modal or modeless HTML dialog box may not be opened in the same process.".
Walkaround:
Send the parent window of the dialog box into the dialog box then use this object open the new window.
example below
Page1.aspx (Suppose it's the parent widow from which you want to open the dialogbox)
<script language=javascript>
function Open()
{
window.ShowModalDialog('WebForm2.aspx', window)
}
</script>
now in WebForm2.aspx, if you want to open another window you use
dialogArguments.window.open('WebForm3.aspx');
in this way, the WebForm3.aspx will still have the values of the session.
Best Regards,