To elaborate further - this is what the top part of my file shows when I open in Notepad (I have blanked my business number) and all I had to change was the RP to RZ - 

<?xml version="1.0" encoding="ISO-8859-1"?>
<Submission xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<T619>
<TransmitterAccountNumber>
<bn15>820000000RP0001</bn15>        This is where I changed the RP to say RZ.   

Hope that makes sense.