I have successfully corrected a balance that is consistently off from month to month by using Maintain Database.  The file is ISBSF.Bxx where xx is the company code.  
First you have to figure the amount off.  And which month it started in or how far back you care to go in months.  I always run the Business status to make sure the balances are up to date before I start editing the balances.  To edit the balances, go to maintain database open up the ISBSF file and choose only the end date and the file you are interested in, in this case APBAL.  Add the amount off to the current balance for each month and enter that into the APBAL field.  YOu might want to do this in a spreadsheet before you start editing.  
Hope this helps.
 
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PS -- Sometimes the dates in the ISBSF file are not in order.  Make sure you are entering the right number into the right date.