C# ตั้งเวลา Timer แล้ว Error ตามรูป ไม่รู้ว่าผิดตรงไหน

private void timer1_Tick(object sender, EventArgs e)
       {
          try{
           string strConn;
           strConn = DBConnString.strConn;
           Conn = new SqlConnection();
           if (Conn.State == ConnectionState.Open)
           {
               Conn.Close();
           }
           Conn.ConnectionString = strConn;
           Conn.Open();

           string sqlShow;
           sqlShow = " SELECT    C_Time ";
           sqlShow += " FROM   iUserCard INNER JOIN tEnter ON substring(iUserCard.C_CardNum,1,50) = substring(tEnter.C_Card,1,50)  ";
           sqlShow += "                             INNER JOIN tUser  ON iUserCard.L_UID = tUser.L_ID ";
           sqlShow += " WHERE  ( SUBSTRING(tUser.C_Unique,1,50) IN  ( SELECT SUBSTRING(Student_ID,1,50)";
           sqlShow += "                                              FROM   tTAD_RegisStudent ";
           sqlShow += "                                              WHERE  Subject_Code = '" + txtSubCode.Text.Trim() + "' AND Semester = '" + txtSemester.Text.Trim() + "' ) ";

           sqlShow += "        AND ( L_TID = '" + txtTerminal.Text + "' ) ";
           sqlShow += "        AND ( C_Date = '" + DateNow + "'         )";
           sqlShow += "        AND ( C_Time >= '" + txtTimeIN.Text.Substring(0, 2) + txtTimeIN.Text.Substring(3, 2) + "00" + "'  ) ";

           sqlShow += "          AND ( scb_flag = 0 ) )";

           com = new SqlCommand();
           com.CommandType = CommandType.Text;
           com.CommandText = sqlShow;
           com.Connection = Conn;
           SqlDataReader dr = com.ExecuteReader();


           if (dr.HasRows)
           {
               ShowDataInOut();
               dgvComeIN.Rows.Clear();
               ShowClassInOut();
               ShowStudentNoPresent();
           }
       }catch(exception ex){ 
        messagebox.show(ex.tostring());
       }finally{
           dr.Close();
      }
       }

   string strConn;
           strConn = DBConnString.strConn;
           Conn = new SqlConnection();
           if (Conn.State == ConnectionState.Open)
           {
               Conn.Close();
           }
           Conn.ConnectionString = strConn;
           Conn.Open();

string sqlShow;
           sqlShow = " SELECT    C_Time ";
           sqlShow += " FROM   iUserCard INNER JOIN tEnter ON substring(iUserCard.C_CardNum,1,50) = substring(tEnter.C_Card,1,50)  ";
           sqlShow += "                             INNER JOIN tUser  ON iUserCard.L_UID = tUser.L_ID ";
           sqlShow += " WHERE  ( SUBSTRING(tUser.C_Unique,1,50) IN  ( SELECT SUBSTRING(Student_ID,1,50)";
           sqlShow += "                                              FROM   tTAD_RegisStudent ";
           sqlShow += "                                              WHERE  Subject_Code = '" + txtSubCode.Text.Trim() + "' AND Semester = '" + txtSemester.Text.Trim() + "' ) ";

           sqlShow += "        AND ( L_TID = '" + txtTerminal.Text + "' ) ";
           sqlShow += "        AND ( C_Date = '" + DateNow + "'         )";
           sqlShow += "        AND ( C_Time >= '" + txtTimeIN.Text.Substring(0, 2) + txtTimeIN.Text.Substring(3, 2) + "00" + "'  ) ";

           sqlShow += "          AND ( scb_flag = 0 ) )";

           com = new SqlCommand();
           com.CommandType = CommandType.Text;
           com.CommandText = sqlShow;
           com.Connection = Conn;
           SqlDataReader dr = com.ExecuteReader();


           if (dr.HasRows)
           {
               ShowDataInOut();
               dgvComeIN.Rows.Clear();
               ShowClassInOut();
               ShowStudentNoPresent();
           }
           dr.Close();