COOKIES - Expecting String Output Issue

I am trying to create a shopping basket in asp and it works in setting the cookie and when it response.writes it sets the correct productID, however i keep getting the error message for the line "Response.Cookies (CookieName) = CookieString" reffering to the CookieName it says it it is expecting a string input, can anybody help please?

<%
dim CookieString
dim CookieName
CookieString = Request.Form("qty")
CookieName = Request.Form("ID")
'Response.Write Cookiename
Response.Cookies (CookieName) = CookieString
%>
<form name="buy" action="quantity.asp" method="post">
<p>Quantity:</p>
<input name="qty" maxlength="2" size="2" />
<input name="ID" style="visibility:hidden" value="<%=ProductID%>"/>
<input type="submit" name="buy" value="buy" />
</form>