ajax cascading dropdown not working -

i using ajax toolkit 4.5. have use cascading dropdown in project. tried this-

 <asp:dropdownlist id="dropdownlist1" runat="server"  width="126px"></asp:dropdownlist>     <asp:cascadingdropdown id="cascadingdropdown1" targetcontrolid="dropdownlist1" category="country" runat="server" usecontextkey="true" prompttext="select" servicemethod="getcountry" servicepath="~/ajaxservice.asmx" ></asp:cascadingdropdown> 

and web service code is-

  public cascadingdropdownnamevalue[] getcountry(string knowncategoryvalues, string category)     {         ajaxdatacontext db = new ajaxdatacontext();         var list = db.countries.select(con => new {con.country1,con.id }).distinct();         list<cascadingdropdownnamevalue> values = new list<cascadingdropdownnamevalue>();         foreach (var data in list)         {             values.add(new cascadingdropdownnamevalue((string)data.country1, data.id.tostring()));         }         return values.toarray();     } 

but not working. no data showing on dropdown. please describe wrong doing. thank you.