Why would it give error "unable to find tax code USA" when creating an invoice in sample data?

Hi Eva,

Is the MultiCurrency Order Entry sample data? This error could occur because USA is the default tax group defined in the OE entry template, and you are trying to enter an order for a non-US customer than does not have a tax group defined. If the tax group on the customer is blank, the code from the entry template will be used, and since the currency is saved on the tax group and must match the customer currency, the error you see is the result.

If you still get this error and think things are OK, please post what the customer currency is, what is the tax group defined on the customer, and what the default tax group on the entry template is.