honestly i don't know what user.html looks like (i don't think i have one in any of my applications.....but i have not used the new wizard yet).
remember that URL items are passed as arguments, and so if you have none then request.args(0) will be None. that HTML file assume that there is at least 1 argument passed to the function, you are now trying to re-use that file as in include/extend for a function/view that does not require arguments and so it's None. you could edit it to check for None before doing the replace if you really need to have that included. good luck! cfh
