Diagnosis
There is a conflict between the taxable country in the decision treedefined in the target parameter (header level) and the country assignedto the decision tree in the IMG sub-activity Assign Decision Tree.

The taxable country in the decision tree must be the same as thecountry assigned in the sub-activity AssignDecision Tree. (contained in the activity Assign Tax Calculation andDetermination Rules)
Either change your taxable country in Define Tax EventDetermination or the country in the activity above so that bothcountries are the same.