Diagnosis
The country used by the TTE has not been defined for tax determination.
Address data is mandatory on Business Partner level and optional on Itemlevel. For tax determination, the address data on the item level takespriority.

System Response

Procedure
In Customizing for TTE
Choose Define Tax Location.
Maintain the required country.
Choose Save.
Adjust the data in your document, as required.
To update Customizing settings, choose ImmediateCustomizing Refresh.