UOM Error in SNC PO XML

When sending ORDERS05 IDOC from ECC, the UOM for product is SF (not FT2). We have set up SF in the TCode CUNI in SNC to mirror FT2 and removed the ISO code from FT2. We should only have one ISO code FTK and it should be associated to SF. However, I am getting the following error when processing the IDOC and/or SAPXML:
     <severity>error</severity>

     <text>Item 00001 net price: Unit of measure for base quantity is invalid</text>