If you get the error:
GST account linked account is missing
when importing into MYOB, check that all your tax codes in MYOB that you are using are linked to an account for tax collected & tax paid.
To do this, in MYOB click Lists > Tax Codes. Open each account that you use and ensure that there is an account allocated to "Linked Account for Tax Collected" and "Linked Account for Tax Paid". If not then you should add the missing accounts.