Redmine

I need help with a redmine. Sometimes application crashes and I can't why. After apache reload redmine goes many days without problems.

Can anybody help me with this problem?

Environment:
Redmine version 2.5.1.stable
Ruby version 1.9.3-p448 (2013-06-27) [x86_64-linux]
Rails version 3.2.17
Environment production
Database adapter Mysql2
SCM:
Subversion 1.6.11
Mercurial 2.2.2
Git 1.7.1
Filesystem
Redmine plugins:
appmenuadds 1.4.2
calendar_shortcut_plugin 0.0.1
project_alias 0.1.0
redmine_message_issues 0.1.0
scrum 0.5.0
--

Started GET "/" for 213.81.172.253 at 2014-08-06 13:51:07 +0200
Processing by WelcomeController#index as HTML
Current user: Ladislav (id=117)
Rendered news/_news.html.erb (2.1ms)
Rendered welcome/index.html.erb within layouts/base (2.6ms)
Completed 500 Internal Server Error in 6.4ms

ActionView::Template::Error (translation missing: en.date.formats.default):
3: <%= "(#{l(:label_x_comments, :count => news.comments_count)})" if news.comments_count > 0 >
4: <br />
5: < unless news.summary.blank? ><span class="summary"><=h news.summary ></span><br />< end >
6: <span class="author"><= authoring news.created_on, news.author %></span></p>
lib/redmine/i18n.rb:60:in `format_date'
lib/redmine/i18n.rb:71:in `format_time'
app/helpers/application_helper.rb:442:in `time_tag'
app/helpers/application_helper.rb:434:in `authoring'
app/views/news/_news.html.erb:6:in `_app_views_news__news_html_erb__3644809541294843667_70358917994100'
app/views/welcome/index.html.erb:8:in `_app_views_welcome_index_html_erb___56145358015715849_70358917874300'