Error while trying to restore DataSource data in DataGridViewComboBoxCell?

I have a DataGridView with two DataGridViewComboBoxColumns. I want to use the selected item in the first column to trigger repopulation of the items in the second column in every row.

Here is the code I have. "addlInfoParentCat" identifies the first column, and currentRow.Cells.Item (1) is the DataGridViewComboBoxCell that I want to repopulate. ExtEventAdditionalInfoType is type I that contains string / value pairs.

Private Sub dgvAdditionalInfo_CellValueChanged(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles dgvAdditionalInfo.CellValueChanged
    Dim currentCell As DataGridViewCell
    currentCell = Me.dgvAdditionalInfo.CurrentCell
    If Not currentCell Is Nothing Then
        If currentCell.OwningColumn.DataPropertyName = "addlInfoParentCat" Then
            Dim parentTypeID As Integer = currentCell.Value

            Dim currentRow As DataGridViewRow = Me.dgvAdditionalInfo.CurrentRow
            Dim subtypeCell As DataGridViewComboBoxCell = currentRow.Cells.Item(1)

            Dim theChildren As New List(Of ExtEventAdditionalInfoType)

            theChildren = Custom_ExtEventAdditionalInfoType.GetChildrenOfThisParentOrderByTypeName(parentTypeID)
            subtypeCell.DataSource = Nothing
            subtypeCell.DataSource = theChildren
            subtypeCell.DisplayMember = "ExtEventAdditionalInfoTypeDescr"
            subtypeCell.ValueMember = "ID_ExtEventAdditionalInfoType"
        End If
    End If
End Sub

      

        
        
        
      

    

Basically I can see that the binding works fine the first time. When I select an item in the first column, it fills in the items in the second correctly. I can add rows to the DataGridView and repeat the process.

The problem comes when I try to change the element of the first column after the second column is already linked. I am getting an endless string of dialog boxes with the following:

System.ArgumentException: The DataGridViewComboBoxCell value is not valid.

Any idea why this is happening? Thanks in advance!

UPDATE The CodeByMoonlight suggestion appears to be working.

I clear the DataGridViewComboBoxCell value before re-binding:

....

            subtypeCell.DataSource = Nothing
            subtypeCell.Value = Nothing  'here the change
            subtypeCell.DataSource = theChildren

....