If you have entered single opening balances on your bank accounts, we recommend that you reconcile the opening balance first. This makes sure the correct Statement opening balance shows on the Bank Reconciliation window.
Open: Cash Book > Period End Routines > Bank reconciliation.
Save the reconciliation and check the report produced.
You should keep the report as part of you financial records. When you start to delete reconciled transactions the value of the deleted transactions is added to the opening balance. Without the first report you cannot identify the opening balance.
You can now continue to reconcile your bank account transactions as normal.