This can be various reasons why the office balance still has a balance, would suggest checking some of the transactions and making sure they are correct.
Check all the bills are correct and weren't billed for more than required and have just been marked off.
Check that there are no duplicate bills and all bills that should of been reversed are reversed on the office ledger, this can be seen easier by looking at the Office ledger tab rather than the all tab.
Check that a posting hasn't posted as a zero balance and should of been a value to pay against the balance.
If the balance is to do with an AD then take a look at the below:
Check if the AD has been billed.
See if the AD can be deleted in the Billing wizard/Accounts Billing if it isn't billed.
If it is billed look at incurring this posting.
If the balance is to do with an expenses balance then take a look at the below:
Check if the Expenses have been billed.
If they haven't been billed can the expenses be deleted in Billing Wizard.
If they can't then you can do a minus expenses posting.
If they have been billed either credit note them or do a minus expenses posting and bill that one.
If these bills are not going to be paid they can then be written off.
If you still can't rectify the balance, please raise a new case online and reference the title of this article.