This comes up at the point where you enter the client’s SIN and name (so, the very start of the process). I select “Certified by…Taxpayer” (see below), then click Next, and the error message appears at the top - above the entry fields.
Just trying to register for a Trust…got the same thing, different code. Playing with the entries there until CRA finally booted me off got me three different error codes…but zero access either. For some reason the Trust has two different numbers and, while it has three Trustees, one has two different names on the materials from CRA. WTAF?