SAP Message CA_TTE619 - Reverse mapping not possible due to ambiguous external value

Diagnosis
The system always checks if a business partner tax group can be mappedbased on an external object assignment. If 2 or more externalassignments exists for 1 internal value, a error message is written tothe TTE trace log.

System Response
Processing terminated.

Procedure
If an external tax group should be mapped, proceed as follows:
Call activity: Assign Objects From ExternalSystems (Cross-Application Components -> Transaction Tax Engine ->Utilities -> Assign Objects From External Systems)
Select the relevant system: systemID1 &V3& systemID2 &V4&, country andtax type &V2&
Check that the TTE internal value &V1& has a unique relation with theexternal value.
Save your entries.
Refresh customizing immediately with the activityImmediate Customizing Refresh.