Prolem with cookies after a postback

So I'm having an issue with my cookie where the value gets mangled after a postback.  I initially create the cookie on the server like this:
 
HttpCookie aCookie = new HttpCookie("emergencyNotification");
aCookie.Values["showYN"] = "true";
aCookie.Values["id"] = msg.EmergencyNotificationId.ToString();
Response.Cookies.Add(aCookie);   The value of the cookie .Values looks like this: showYN=true&id=11 Then, on the client-side, I respond to a click event and run some javascript to change the showYN key to false. In Javascript I pop up alerts that tell me the value of my cookie and everything looks fine. Then I do a postback and read the .Values of the cookie aga ...