Send two additional parameter to wcf service from autocompleteextender

<div>Dear frends,</div> <div>
</div> <div>I want to Send two aditional parameter to wcf service from autocompleteextender.</div> <div>for that i used code written below:</div> <div>
</div> <div><script type = "text/javascript"></div> <div>    function SetContextKey() {</div> <div>        $find('<%=AutoCompleteExtender1.ClientID>%').set_contextKey($get("<%=ddlCountries.ClientID %>").value);</div><div>    }</div> <div></script></div> <div><asp:TextBox ID="txtContactsSearch" runat="server" onkeyup = "SetContextKey()"></asp:TextBox></div><div> <div></div> <div><cc1:AutoCompleteExtender ServiceMethod="SearchCustomers"</div> <div>    MinimumPrefixLength="2"</div><div>    CompletionInterval="100" EnableCaching="false" CompletionSetCount="10"</div> <div>    TargetControlID="txtContactsSearch" UseContextKey = "true"</div><div>    ID="AutoCompleteExtender1" runat="server" FirstRowSelected = "false"></div> <div></cc1:AutoCompleteExtender></div><div>
</div> <div>and my wcf service contain function </div> <div> <div></div> <div>public static List<string> SearchCustomers(string prefixText, int count, string contextKey,string ID)</div> <div>{</div> <div>}</div> <div>
</div> <div>but still I am getting null value in contextkey parameter in SearchCustomer method.</div> <div>
</div> <div>Plz help me to resolve this issue asap.</div> <div>
</div> <div>thanx in advance.</div> </div>
</div>