"Permission Denied" when attempting to set the value SO Header UDF

I am on 4.3 and am using BOI in Access VBA to update some fields on Sales Orders (headers only).  I have a UDF field for Sales Order shipping priority.  UDF_Priority is a drop box field with a length of 20 with 3 options: Staging, Expedited, and Normal (default).

All the other fields update properly, but when it gets to this line, it fails with "Permission Denied"

bSuccess = objPVXData.nsetvalue("UDF_PRIORITY", rstSOList!priority)

I have verified that the value in the field rstSOList!priority is appropriate ('Normal').  What am I missing?