Before investigating, confirm that the expected balance does disagree with the transactional balance.
If the affected nominal account is a year end account, the difference may be due to the year end process. Access Financials does not show the transactions that make up the year end, so the difference could be from the transference of balances into this account.
Check this by running the Year End Journal report: click Financials, then click Reports, then click Transactions. Use the reference YEARXXYY, where XX and YY are the years of your previous year end.
If this is not a year end account or the issue persists after checking, contact the support team to investigate. If you have trouble reaching us, see Get support in Access Financials.