PL/SQL中带有返回值的函数怎么在C#中调用？

PL/SQL中的函数及其参数如下：
PACKAGE:U1BP.pxf000bdzrf
FUNCTION getEcCheckBDW31(
         p_co VARCHAR2,                                       IN==> 公司
        p_empid VARCHAR2,                                 IN==> 员工代号
         p_boffid VARCHAR2,                                   IN==>差假代号
         p_frday VARCHAR2,                                   IN==>差假起日
         p_frhh VARCHAR2,                                    IN==>差假起时
         p_today VARCHAR2,                                   IN==>差假迄日
         p_tohh VARCHAR2,                                    IN==>差假迄时
         p_dys NUMBER,                                        IN==>日数
         p_hrs NUMBER,                                        IN==>时数
         p_nl VARCHAR2,                                       IN==>NL纪录，N表示正常，L表示删除
         p_odupz VARCHAR2,                                  IN==>出勤厂区
         p_odudp VARCHAR2,                                 IN==>出勤部门
         p_ajmk VARCHAR2,                                   IN==>调整注记
         p_boffidclass VARCHAR2)                           IN==>差假代号类别，固定为BOFFID
 RETURN VARCHAR2                                           OUT==> 回传的错误讯息
我对应写的C#代码如下：
public static void ChaiJiaDan(int flag, string strName, params Object[] paras)//主表传入ERP方法,接受两个参数，第一个是文档所提供的传ERP存储过程
        {
            constring[0] = "server=bhhg;uid=u1bs2;pwd=u1bs2";
            constring[1] = "server=bhzy;uid=u1bs2;pwd=u1bs2";
            constring[2] = "server=bhfd;uid=u1bs2;pwd=u1bs2";
            constring[3] = "server=bhgj;uid=u1bs2;pwd=u1bs2";
            //第二个参数是接收一个数组，该数组里面是对应的表单字段
            using (OracleConnection conn = new OracleConnection(constring[flag]))//数据库连接字符串
            {                OracleCommand cmd = new OracleCommand(strName, conn);//创建一个执行语句的对象
                OracleParameter[] para = new OracleParameter[]
                {
                    new OracleParameter("p_co",OracleType.VarChar),             //以下为ERP接收的字段，跟文档上保持一致
                    new OracleParameter("p_empid",OracleType.VarChar),
                    new OracleParameter("p_boffid",OracleType.VarChar),
                    new OracleParameter("p_frday",OracleType.VarChar),
                    new OracleParameter("p_frhh",OracleType.VarChar),
    
                    new OracleParameter("p_today",OracleType.VarChar),
                    new OracleParameter("p_tohh",OracleType.VarChar),
                    new OracleParameter("p_dys",OracleType.Number),
                    new OracleParameter("p_hrs",OracleType.Number),
                    new OracleParameter("p_nl",OracleType.VarChar),                    new OracleParameter("p_odupz",OracleType.VarChar),
                    new OracleParameter("p_odudp",OracleType.VarChar),
                    new OracleParameter("p_ajmk",OracleType.VarChar),
                    new OracleParameter("p_boffidclass",OracleType.VarChar)
                  
                
                };                for (int i = 0; i < paras.Length; i++)
                {                    para[i].Value = paras[i];                }                cmd.Parameters.AddRange(para);                OracleParameter res = new OracleParameter("wrk_message", OracleType.VarChar, 100);
                res.Direction = ParameterDirection.ReturnValue;
                cmd.CommandType = CommandType.StoredProcedure;
                conn.Open();
                cmd.ExecuteNonQuery();                                      //执行传ERP操作
                string temp = res.Value.ToString();                if (temp != "")                                               //判断是否操作成功
                {
                    throw new Exception(string.Format("未执行成功,错误代号是{0}", temp));
                }
                conn.Close();
            }        }执行老是报错！说“不是过程或函数未定义”
求大神帮忙解决！