Redmine

Hi,

I have a fresh installation of Redmine 2.5.2 on an Ubuntu server (virtual machine). I have several plugins installed and everything seems to work fine (it took me two days to reach this point) except the LDAP authentication.
I had configured the authentication yesterday and everything was working fine. This morning I have switched the DB to postgresql because I want to import a previous Redmine installation (performed by another person), and LDAP stopped working (even though the parameters are the same). Even more strangely, I have installed the LDAP synchronization plugin and it works perfectly.
Here are the errors I get:

• In authentication modes, if I press "test", I get
  

  Unable to connect (private method `timeout' called for #)
  

• In production.log, I have
  

  Started GET "/auth_sources/3/test_connection" for 127.0.0.1 at 2014-09-19 13:18:21 +0200
  Processing by AuthSourcesController#test_connection as HTML
    Parameters: {"id"=>"3"}
    Current user: admin (id=1)
  Redirected to http:// ** SRV ADDR HERE ** /auth_sources
  Completed 302 Found in 8.3ms (ActiveRecord: 1.6ms)
  Started GET "/auth_sources" for 127.0.0.1 at 2014-09-19 13:18:21 +0200
  Processing by AuthSourcesController#index as HTML
    Current user: admin (id=1)
    Rendered auth_sources/index.html.erb within layouts/admin (5.8ms)
    Rendered admin/_menu.html.erb (3.5ms)
    Rendered plugins/redmine_code_review/app/views/code_review/_html_header.html.erb (0.0ms)
    Rendered plugins/redmine_code_review/app/views/code_review/_body_bottom.html.erb (0.0ms)
    Rendered layouts/base.html.erb (18.9ms)
  Completed 200 OK in 36.6ms (Views: 26.4ms | ActiveRecord: 4.5ms)
  

• If I try to login with a valid LDAP user (it worked smoothly yesterday):
  

  Started POST "/login" for 127.0.0.1 at 2014-09-19 13:01:37 +0200
  Processing by AccountController#login as HTML
    Parameters: {"utf8"=>"✓", "authenticity_token"=>" ** TOKEN HERE ** ", "back_url"=>"http:// ** SRV ADDR HERE ** /", "username"=>" ** USERNAME HERE ** ", "password"=>"[FILTERED]", "login"=>"Connex\
  ion »"}
    Current user: anonymous
  Completed 500 Internal Server Error in 11.0ms
  
  NoMethodError (private method `timeout' called for #<AuthSourceLdap:0x007f764db37a20>):
    app/models/auth_source_ldap.rb:95:in `with_timeout'
    app/models/auth_source_ldap.rb:41:in `authenticate'
    app/models/user.rb:271:in `check_password?'
    app/models/user.rb:177:in `try_to_login'
    app/controllers/account_controller.rb:191:in `password_authentication'
    app/controllers/account_controller.rb:186:in `authenticate_user'
    app/controllers/account_controller.rb:40:in `login'
  

I've tried googling for several hours, but without luck...
Do you have any idea about why this happens and how to solve the problem?
Thanks a lot in advance!
Rob