Problem in web Service.(web method)

hi frnds..
I m using a web method for AutocompleateExtender...& i want to pass 2 arguments....
Plz see my code-
[WebMethod]
        public string[] GetStateInfo(string prefixText,int Countryid)
        {

            DS = obj_cDataAccess.RunSPReturnDataSet("SP_STATE_GETNAME",
                                 new SqlParameter("@PREFIX", prefixText),
                                 new SqlParameter ("@COUNTRYID",Countryid));
...