Datagridview combobox column problem

I have a grid that has a column of comboboxes.  I'm pulling from a database for three separate conditions and filling three datasets.  I want to bind these datasets to one particular column, but only every third cell.  In other words, row one should bind to ds1, row 2 to ds2, row 3 to ds3, row 4 to ds1, row 5 to ds2, etc.

I am doing this

        For rw As Integer = 0 To 23 Step 3
            Dim cell As New DataGridViewComboBoxCell
            cell.DataSource = dsslide1
            dgvNewJob.Rows(rw).Cells(1) = cell
         Next

        For rw As Integer = 1 To 23 Step 3
            Dim cell As New DataGridViewComboBoxCell
            cell.DataSource = dsslide1
            dgvNewJob.Rows(rw).Cells(1) = cell
         Next

I get errors and the box does not contain any data.

Any ideas what I am doing wrong?