Even though I filed a bug report #8257 about my problem, maybe someone here can point me to a solution.

After porting a site from chiliproject via openproject 2.4.0 to 3.0.3 some wiki pages did not work.
These pages report an “internal error” and the production log shows this when I try to open a wiki page called “Einen_Branch_bearbeiten”:

Started GET "/projects/webseiten/wiki/Einen_Branch_bearbeiten" for 134.102.xxx.yyy at 2014-05-26 16:34:01 +0200
Processing by WikiController#show as HTML
  Parameters: {"project_id"=>"webseiten", "id"=>"Einen_Branch_bearbeiten"}
  Rendered wiki/_content.html.erb (8.0ms)
  Rendered wiki/show.html.erb within layouts/base (43.2ms)
Completed 500 Internal Server Error in 73.3ms

ActionView::Template::Error (wrong number of arguments (2 for 1)):
    28: ++#%>
    29:
    30: <div class="wiki wiki-content">
    31:   <%= textilizable content, :text, :attachments => content.page.attachments %>
    32: </div>
  lib/redmine/wiki_formatting.rb:60:in `[]'
  lib/redmine/wiki_formatting.rb:60:in `to_html'
  app/helpers/application_helper.rb:554:in `textilizable'
  app/views/wiki/_content.html.erb:31:in `_app_views_wiki__content_html_erb___2784804701036560664_62076940'
  app/views/wiki/show.html.erb:78:in `_app_views_wiki_show_html_erb__4185142407771794213_65399620'

After some testing I narrowed it down to a size limit for a wiki page of exactly 2048 characters.
I get the same error if I add another character directly in the textfield of that page in the wiki_contents table of the database.

It is possible to edit the page by adding /edit the its link. But saving it only helps if the number of characters is low enough.

The problem does not accur on an (hopefully) identical system (Debian 7, Apache, MySQL) with a fresh install of OpenProject 3.0.3.