Diagnosis
You can not combine the 3.0 Tax Determination with the TaxEvent TaxDetermination for tax codes. The latter was introduced in release 4.0and if you want to use it, you must not use the 3.0 Tax Determinationbut the 4.0 Tax Determination.

Procedure
Do not enter the tax code oder switch to the 4.0 Tax Determination.
Enable / Disable 3.x TTE Tax Determination
Define Tax Event Determination
Assign Tax Event Determination and CalculationRules
Define Tax Code and Account Determination Key