Hi Mullin
The issue you are experiencing may be due to duplicate entries in the
customizing for tax classifications in the R/3 system. Kindly check
your mapping tables (transactions PITM and PITC).
Be aware that there should only be ONE tax class per tax type.
After correcting the customizing start the initial download
of DNL_CUST_TAX again.
You may also check your customizing :
Customer Relationship Management / Basic Functions / Taxes /
Basic Settings / Tax Types and Tax Groups /
Assign Tax Groups to SAP ECC Tax Classifications (Business Partner)
Best Regards
James