将参数值从 sqlparameter 转换到 string 失败

Question

c#中调用SQL server的procedure,报"将参数值从 sqlparameter 转换到 string 失败";
      
 System.Data.SqlClient.SqlParameter[] sp = new System.Data.SqlClient.SqlParameter[] 
            {    
                new SqlParameter("@v_RecId",strRecId),                //入库单号
                new SqlParameter("@v_Quantity",strQuantity),          //数量
                new SqlParameter("@v_GR_Rcpt",strGR_Rcpt),            //收货者
                new SqlParameter("@v_Idate",strIdate),                //入库时间
                new SqlParameter("@v_duoList",strDuoList)             //List传入的值:2334,2345,455,567
              };            Database db = DBHelper.getDatabase("DBinstance");
            using (DbConnection conn = db.CreateConnection())
            {
                conn.Open();
                DbTransaction tran = conn.BeginTransaction();
                int i = db.ExecuteNonQuery(tran, "Proc_Stock",sp);
                ID=GetID(strRecID);//调用方法取得ID
                                if (ID!=null)
                     tran.Commit();
                 else
                     tran.Rollback();
            } procedure用程序中取得的数据测试是没问题的，请高手指点.