This issue comes from a reconciled item having a date that is before the brought forward date, you will need to do amend the dates on the reconciled column:
From the main menu go into the Bank Reconciliation.
Select the correct bank and statement number.
Check the date on the statement is the correct brought forward and bank rec date.
Go on the Reconciliation tab.
Find the items in question with the incorrect date.
Manually amend the dates in the Statement Date column.
Once these are done it should allow the selection of the unreconciled items in the drop down at the top.