Try seeing if you can stop it in the RowDeleting instead because after it comes RowDeleted
this.QuoteQty_Column.RowDeleting += new DataRowChangeEventHandler(this.QuoteQty_RowDeleting);
private void QuoteQty_RowDeleting(object sender, DataRowChangeEventArgs args)
{
if (QuoteQty_Column.Rows[modRowIndex].RowState.ToString() != "Deleted")
{
// Just a snippet from something else; conceptual try looking up the RowDeleting Event
}
}