深层的数据库类型异常？高手来

深层的数据库类型错误？高手来
我运行getspdt方法的时候会报错：System.Data.SqlClient.SqlInternalConnectionTds 无法强制转换成System.Data.SqlClient.SqlInternalConnectionSmi

存储过程都参数都是varchar，在数据库里面执行没问题。

C# code

SqlConnection scn = new SqlConnection();//连接设定    Access acc = new Access();   //操作基础类    string beginDate = "";    string enddate = "";    string txtUserid = "";    /// <summary>    /// 国际惯例取字符串    /// </summary>    ///<param name="scn">连接的SqlDataConnection</param>    private void getscnstr(SqlConnection Scn)    {        if (scn.ConnectionString == "")        {            Scn.ConnectionString = acc.ScnConnStr;        }    }    /// <summary>    /// 国际惯例芝麻开门    /// </summary>    /// <param name="scn">连接的SqlDataConnection</param>    private void OpenConn(SqlConnection Scn)    {        if (scn.State == ConnectionState.Closed)        {            Scn.Open();        }    }    private void MessageBoxShow(String Errstr)//信息提示    {        Response.Write("<scr" + "ipt> alert('" + Errstr + "') </scr" + "ipt>");    } private DataTable GetSpdt(out DataTable spdt,string seUserid,string BeginDate,string Enddate)    {        try        {            spdt = null;            string Userid = (string)(Session["LoginUser"]);            string UserAuthority = (string)(Session["Authority"]);            getscnstr(scn);            OpenConn(scn);            string sqlstr2 = "SELECT * FROM uvw_IsPrincipal WHERE FnAME='" + Userid + "' AND IsPrincipal=1 ";            DataTable dt2 = acc.GetSereachData(scn, sqlstr2);            if (dt2.Rows.Count == 0)            {                    seUserid = Userid;            }            getscnstr(scn);            OpenConn(scn);            SqlCommand cmd = new SqlCommand();            cmd.CommandText = "usp_DalayReoprt";            cmd.CommandType = CommandType.StoredProcedure;            cmd.Connection = scn;            cmd.Parameters.Add("@PositionCode", SqlDbType.VarChar);            cmd.Parameters["@PositionCode"].Value = UserAuthority;            cmd.Parameters.Add("@Code", SqlDbType.VarChar);            cmd.Parameters["@Code"].Value = "'%"+seUserid+"%'";            cmd.Parameters.Add("@BeingDate", SqlDbType.VarChar);            cmd.Parameters["@BeingDate"].Value = "'"+BeginDate+"'";            cmd.Parameters.Add("@EndDate", SqlDbType.VarChar);            cmd.Parameters["@EndDate"].Value = "'" + Enddate + "'";            SqlDataAdapter sda = new SqlDataAdapter(cmd);            //DataTable DDT = new DataTable();            //DataSet ds=new DataSet();            sda.Fill(spdt);            //spdt = ds.Tables[0];            return  spdt;        }        catch (Exception ex)        {            MessageBoxShow(ex.ToString());            spdt = null;            return spdt;        }            }

C# code

 private void getscnstr(SqlConnection Scn)    {        if (scn.ConnectionString == "")        {            Scn.ConnectionString = acc.ScnConnStr;        }    }