Bill of Distribution CSV Import Error

I am trying to update existing item records, changing the Location Supply Type from Build to Transfer, and populating the Distribution Network and Distribution Category fields with values.  The CSV Import tool does not list the latter two fields in the mapping options.  My test file results in error; When supply type of transfer is used for a location, that location must have an associated Bill of Distribution. Please define a Bill of Distribution for that location. 

I have a Bill of Distribution set up for the location, so I do not understand why I am getting this error.  The Distribution Network and Distribution Category fields are editable on my preferred item forms and the fields are set up, so again, I am not sure why they are not available for mapping.  The attachment is a bit small, but reflects how everything is set up.