I file T4 returns for clients using Quickbooks desktop. I received the same error. I had to edit the XML file that QB desktop creates. QB desktop uses the company file client name as transmitter and the client business number as transmitter. I opened the file in Notepad and entered my business number and name as transmitter and my RepID. The file then was accepted with no issues. I see this as a QB problem, not CRA. Can't get through to CRA anyway.