If the column you are reading has the potential for a NULL value, then you must use the DBNull object:
DataRowView dRowView = m_SchedCommentsBindingSource[0] as DataRowView;
dsL2DB.SchedulesRow SchedRow = dRowView.Row as dsL2DB.SchedulesRow;
sDeleteComment = (SchedRow["DeleteComment"] == DBNull.Value ? "No Delete Comment" : SchedRow.DeleteComment);
More generically:
If (ds.Rows[0]["ColumnName"] == DBNull.Value)
{
// Do something for NULL value
}