Use session variable to do it.
Declare this in both aspx.cs file:
public String SessionStore
{
get { return (String)(Session["MyData"]) ?? ""; }
set { Session["MyData"] = value; }
}
In current page, set it to some value:
SessionStore = "abc";
In the target page, get it:
var value = SessionStore;
Hope this help.
Cheers