Nullreference error (Object reference not set to an instance of an object.)

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Hi all, im having mad problems here...i have a datagrid that i have added two new columns of unbound data. I want to make it work so that it displays given name and last name in a table that only has ID and other information so that the viewer knows what information belongs to who.
this is the original code for events which works

private void addColumnDataToEventInvitees()
        {
            // Load in custom columns for event invitees fNames and lNames
            if (dgvEvents.Rows.Count > 0 && dgvEventInvitees.Rows.Count > 0)
            {
                for (int i = 0; i < dgvEventInvitees.Rows.Count; i++)
                {
                    DataGridViewRow selectedRow = dgvEventInvitees.Rows[i];
                    int personID = Convert.ToInt16(selectedRow.Cells[0].Value);

                    DataRow findRow = data.Tables["People"].Rows.Find(personID);

                    dgvEventInvitees["GivenNames", i].Value = findRow["GivenNames"].ToString();
                    dgvEventInvitees["LastName", i].Value = findRow["LastName"].ToString();
                }
                peopleEventTableAdapter.Fill(data.PeopleEvent);
            }
        }

this is my very similar code but it is for the medical forms. I have looked at blogs and i hear talk of adding a

new

instance of the object

I am just not sure how to implement this...Any help would be great!!
the error pops up in here. It says "there is already an open datareader associated with this command which must be closed first"

it tells me to close the datareader but i can't figure out how to close it :(

private void personnameToDataGrid()
        {
            if (dgvMedical.Rows.Count > 0)
            {
                for (int i = 0; i < dgvMedical.Rows.Count; i++)
                {
                    DataGridViewRow selectedRow = dgvMedical.Rows[i];
                    int personID = Convert.ToInt16(selectedRow.Cells[0].Value);

                    DataRow findRow = data.Tables["People"].Rows.Find(personID);

                    dgvMedical["MDGivenNames", i].Value = findRow["GivenNames"].ToString();
                    dgvMedical["MDLastName", i].Value = findRow["LastName"].ToString(); //my error was appearing on this //line
                }
                medicalTableAdapter.Fill(data.Medical);

            }
        }