Can't change line through EDI 860

I'm testing through direct keying into P47130.  I am able to Add a line to an existing sales order.  When I try to use change code QI or QD, I receive the following error:

The record being processed either already exists for an 'ADD'

               function or does not exist for an 'INQUIRY', 'CHANGE' or

               'DELETE' function

I suspect some of my mapping is off.  I'm putting the increased or decreased amount in the UORG field and the item number in LITM, with TPUR = 4.   I closely followed the required fields in document 1340444.1.

What am I missing?

Just a note that I'll be out of the office on Monday and Tuesday, so I may not see any replies until Wednesday.  Thanks!