C#

InvalidOperationException was unhandled:
Missing the DataColumn 'PD_Program_Name' in the DataTable 'ProgramDetails' for the SourceColumn 'PD_Program_Name'.

NullReferenceException was unhandled
Object reference not set to an instance of an object.

public openForm callbackOpenForm;
public DisplayProgramNameDate callbackProName;
public openExistingProgram callbackExistProgram;

public formA{}

private void btnOpen_open_Click(object sender, EventArgs e)
{
    callbackProName(cboProgram_open.Text, Convert.ToString(DateTime.Now));
    callbackOpenForm("ProgramSetting");
    callbackExistProgram();  <----------------------error on this delegate
    this.Hide();
}

public formB{
          formA fA = new formA();
          fA.callbackExistProgram += new openExistingProgram(this.callbackExistProgramFn);
        }

        private void callbackExistProgramFn()
        {
            sqlconn.DbConnection();
            ds = sqlconn.SelectSQL("ProgramSetting", "PS_Program_Name", singleton.ProName);
        }

//create new drawing area at main
public delegate void CreatePictureBox(Boolean b);
//display pro name in statusstrip at main
public delegate void DisplayProgramNameDate(String sName, String sDate);
//call to open form
public delegate void openForm(String sName);
//Open a program
public delegate void openExistingProgram();