Hi baddoctor62
You are not going to find a fix on the forum - if the simple fixes don't work (and they often don't) - this means the file has a corruption and needs to be repaired by MYOB. Their code is doing something wrong at a particular point or as a result of some specific transactions. MYOB themselves don't know what causes this, however once caused, the corrupt data needs to be manually removed, balance restored, transaction re-entered. There are other parties that can fix MYOB files however they would charge a fee, whereas MYOB should repair this for free.
Regards
Gavin