Check your nominal ledger for debtors (1100) and creditors (2100) at a given date (month end/year end). Now go to Customers, reports, aged debtors reports, aged debtor analysis. Make sure you put the period end date in AND tick the box that says 'exclude later payments'. Hopefully the figure from the report will match the Nominal balance. Of course tyou can now go through the individual accounts balances and reconcile to customer statements. Same applies with Creditors via Purchase ledgere reports.