Redmine

After migrato to 2.4 to 2.6 I receive the follow error message.

Processing by UsersController#index as HTML
  Current user: admin (id=1)
  Rendered users/index.html.erb within layouts/admin (8.7ms)
Completed 500 Internal Server Error in 22.9ms

ActionView::Template::Error (undefined method `mail' for #<User:0x0000000525a8c8>):
       40:   <td class="username"><%= avatar(user, :size => "14") %><%= link_to h(user.login), edit_user_path(user) %></td>
        41:   <td class="firstname"><%= h(user.firstname) %></td>
       42:   <td class="lastname"><%= h(user.lastname) %></td>
       43:   <td class="email"><%= mail_to(h(user.mail)) %></td>
       44:   <td class="tick"><%= checked_image user.admin? %></td>
       45:   <td class="created_on"><%= format_time(user.created_on) %></td>
       46:   <td class="last_login_on"><%= format_time(user.last_login_on) unless user.last_login_on.nil? %></td>
    app/views/users/index.html.erb:43:in `block in _app_views_users_index_html_erb__887442556466231082_50281760'
    app/views/users/index.html.erb:38:in `each'
    app/views/users/index.html.erb:38:in `_app_views_users_index_html_erb__887442556466231082_50281760'
    app/controllers/users_controller.rb:55:in `block (2 levels) in index'
    app/controllers/users_controller.rb:52:in `index'

The same error occurs when I try to access "My account", "issue_statuses" and "users" (the last two from administration)

my config

sh: svn: not found
sh: darcs: not found
sh: hg: not found
sh: cvs: not found
sh: bzr: not found
sh: git: not found
Environment:
Redmine version 2.6.8.stable
Ruby version 1.9.3-p551 (2014-11-13) [x86_64-linux]
Rails version 3.2.22
Environment production
Database adapter Mysql2
SCM:
Filesystem
Redmine plugins:
no plugin installed

I follow this tutorial http://www.redmine.org/projects/redmine/wiki/RedmineUpgrade