Changing user role inside a project doesn't work.
All other parts seems to work, only this button (POST action) failed (nothing happen).

I guess that the problem is around sub-URI.

+Installation+

Environment:
  Redmine version                          2.3.0.stable.11691
  Ruby version                             1.9.3 (x86_64-linux)
  Rails version                            3.2.13
  Environment                              production
  Database adapter                         Mysql2
Redmine plugins:
  no plugin installed

I use Apache and Apache passenger module with some special configuration to deal with sub-URI (@www.myserver.fr/redmine@). Based on http://www.redmine.org/projects/redmine/wiki/HowTo_Install_Redmine_in_a_sub-URI and http://www.redmine.org/issues/11881 In @config/environment.rb@:

[...]
# SUB-URI
# http://www.redmine.org/issues/11881
RedmineApp::Application.routes.default_scope = '/redmine/'

# Initialize the rails application
RedmineApp::Application.initialize!

# Prendre en compte le SUB-URI
Redmine::Utils::relative_url_root = "/redmine/" 

+Request that failed when i press button "change" (tab "Members" inside a project)+
The "Request URL" is false. Should be something like "http://www.myserver.fr/redmine/memberships/1238", no ?

Request URL:       http://www.myserver.fr/memberships/1238
Request Method:    POST
Status Code:       HTTP/1.1 404 Not Found

Request Headers
X-Requested-With:XMLHttpRequest
X-CSRF-Token:ZeR7gqPo/fXMhPJa0IOIJFdWN335/VthcLUwAPaAvDw=
User-Agent:Mozilla/5.0 (X11; Linux x86_64; rv:20.0) Gecko/20100101 Firefox/20.0 Iceweasel/20.0
Referer:http://www.myserver.fr/redmine/projects/meta-archeo/settings
Pragma:no-cache
Host:www.myserver.fr
DNT:1
Content-Type:application/x-www-form-urlencoded; charset=UTF-8
Content-Length:176
Connection:keep-alive
Cache-Control:no-cache
Accept-Language:fr-fr,fr;q=0.8,en-us;q=0.5,en;q=0.3
Accept-Encoding:gzip, deflate
Accept:*/*;q=0.5, text/javascript, application/javascript, application/ecmascript, application/x-ecmascript