You need to determine how the ASP.Net application propagates session ID. It could be a session ID embedded to URL or (most probably) a cookie.

Cookie can be added to HTTP request this way:

pd4ml.setCookie( “JSESSIONID”, cookieValue );
where cookieValue is something like that: “9034657927465;path=/”

JSESSIONID keyword is specific for Java, .Net uses anything else.