Hi Sancti,
This is a common problem with the error reporting system of B1, both in the client and with the SDK.
With the SDK we work around this problem by simply performing our own prechecks before adding a cardcode or an item to the document.
You can use a function with a query, or you can use the Item or BusinessPartner object's GetByKey method. Either way, you should check that the item exists, if it is frozen, and if there is a price for the given cardcode. And you can check for any other rules that you may have.
Regards,
Johan