title: I have an error with Backlogs plugin in Redmine
body: <p>Since last week, I have a problem using <code>redmine_backlogs</code> plugin in Redmine. When I try to log time on an issue, I have this error message: </p>
  
  <p><em>an error occured, please check the server logs (Unprocessable Entity)</em></p>
  
  <p>Checking <code>production.log</code>, I have these lines:</p>
  
  <p><code>ActiveRecord::RecordInvalid (Validation failed: Temps passé n'est pas valide):
    plugins/redmine_backlogs/lib/backlogs_activerecord_mixin.rb:38:in journalized_update_attributes!'
    plugins/redmine_backlogs/app/models/rb_task.rb:138:in update_with_relationships'
    plugins/redmine_backlogs/app/controllers/rb_tasks_controller.rb:28:in update'
    lib/redmine/sudo_mode.rb:63:in sudo_mode'</code></p>
  
  <p>Here are the information about my Redmine instance:</p>
  
  <pre><code>Environment:
  
    Redmine version                3.4.5.stable
  
    Ruby version                   2.2.4-p230 (2015-12-16) [x86_64-linux-gnu]
  
    Rails version                  4.2.8
  
    Environment                    production
  
    Database adapter               Mysql2
  
  SCM:
  
    Subversion                     1.9.3
  
    Mercurial                      3.7.3
  
    Git                            2.7.4
  
    Filesystem                     
  
  Redmine plugins:
  
    a_common_libs                  2.1.10
  
    clipboard_image_paste          1.10
  
    global_roles                   2.1.0
  
    google_analytics_plugin        1.0.0
  
    redmine_backlogs               v1.0.6
  
    redmine_code_review            0.7.0
  
    redmine_dmsf                   1.5.7 devel
  
    redmine_drafts                 0.2.0
  
    redmine_issue_templates        0.1.1
  
    redmine_ldap_sync              2.0.8.devel.gf831737c23
  
    redmine_my_page                0.1.10
  
    redmine_scm                    0.5.1
  
    redmine_xls_export             0.2.1.t9
  </code></pre>
  
  <p>Thank you for your help</p>
  
  <p>Mathieu</p>