I did call CRA yesterday and apparently I was trying to upload the T5018 xml file through RZ0001 (T5 Slips) when I should have been uploading through the RZ0002 portal for Contract Payments.
It was strange because I have in the past always used the payroll portal to upload even the T5018 file. So, I think this RZ0002 account was not there before, at least I don't remember seeing it in the CRA Represent a client account.
In Profile I changed the Business number on the Info page to RZ0002 as well as the business number in the Efile - Options section. It worked!! PTL!
