A common problem when transferring orders to Tripletex is that the VAT codes used in the orders have not been enabled in Tripletex.
Tripletex will not accept these orders unless the corresponding VAT types are enabled in its settings.
This can be done under:
Accounts -> Settings -> VAT Settings -> Global VAT Settings
The screenshot below shows how to enable VAT code 5:
Tripletex provides a list with information on the different VAT codes here: