Question mark problem

Hi to everyone! I'm making a CMS based on Codeigniter for a project. But I've a (maybe, I don't know) "big" problem.

I've a database with some users registered. Some of these has the ? in their name and when I go to their profile page I see "404 Not Found".

Now, I load profile in this way: (the controller)

PHP Code:

public function view($username){ 


and I did a route:

PHP Code:

$route['profile/(:any)'] = "profile/view/$1"; 


Instead: if the username is ?ABC, I'll have 404 on exxample.com/profile/?ABC.
I think that I allowed the ? in the permitted_uri:

PHP Code:

$config['permitted_uri_chars'] = 'a-z 0-9~%.:_\-?'; 


Do you have some idea to solve my problem? thank you!