We cannot convert files with multi-currency transactions. If multi-currency has not been used, there is a possibility that you may be able to turn it off or you can convert the transactions to the native currency.
Multi-Currency in MYOB
If multi-currency has not been used in the file then there is a possibility that you may be able to turn off this feature and re-submit the file for conversion. You will need to have the ability to make adjustments in the MYOB file. Adjustments can not be made if you have the 'Read only' access.