opps sorry my mistake, I failed to see you said 2 different columns, try this:
1) Create a query and insert the same table in twice.
2) Join the 2 different dates from each table.
3) Select 'Totals' and save the query as DuplicateDates.
4) Then create a new 'Unmatched Query' to compare one of the dates in your table to the date in your DuplicateDates query.