That is very odd.  When I try to enter a different surname on my own tax return (where I previously downloaded data from CRA), as long as I tick the box on the info screen (do you want to change the name), I do not get that error code.  When it says to "enter 2", it is referring to the binary  codes or something like that, I think.  By checking the box, you are changing the default value from "1" to "2".  Did the client maybe previously change their name with CRA?