Deleted Cookies - What's happening?

Hello to all.

Here is my problem.
First, I create a cookie this way:

Code:

---

<%
Response.Cookies (" MyCookie")(Request.Querystring("lastname ")) = Request.Querystring("firstname ") Response.Cookies (" MyCookie").Expires = DateAdd("m ", 1, Now())
%>

---

So that in the cookie I make an equality between the name and the first name. The expiry is set to one month. Then in another page, I would like to add some information to the cookie:

Code:

---

<%
Response.Cookies (" MyCookie")(Request.Querystring("Hobby ")) = Request.Querystring (" Period ")
%>

---

Equality between his hobby and how often this person plays it.

But my second code makes disappear (removes) the cookie on client computer... Would somebody have an idea?
Thank you in advance.