Redmine

Hello everybody,

i hope i can get some help in this forum. I have a problem with my redmine installation, after migrating to a different server and a newer version.
unfortunately, i only get the assets (files & themes) and a sqlite.db - File from my old hoster, where i had a redmine 2.4 installation. I migrate the .db file to sql and import it at my new server (Bitnami & Amazon AWS, Redmine 3.1 (but i even tried with 2.6 and get the same error)) to the MySQL-DB. I don't use any plugins.

I think that this works, because
ruby bin/rake db:migrate RAILS_ENV=production

works fine and does all the migration jobs for the Database.

after going to redmine, i first see a correct installation, but after logging in, i get the internal 500 error.
Here is my production.log:

Redirected to http://jipido.bitnamiapp.com/redmine/projects
Completed 302 Found in 9ms (ActiveRecord: 2.9ms)
Started GET "/redmine/projects" for 84.130.194.90 at 2015-09-12 09:39:39 +0000
Processing by ProjectsController#index as HTML
  Current user: admin (id=1)
  Rendered projects/index.html.erb within layouts/base (12.0ms)
Completed 500 Internal Server Error in 97ms (ActiveRecord: 2.3ms)

ActionView::Template::Error ((<unknown>): found character that cannot start any token while scanning for the next token at line 2 column 27):
     9: <%= favicon %>
    10: <%= stylesheet_link_tag 'jquery/jquery-ui-1.11.0', 'application', :media => 'all' %>
    11: <%= stylesheet_link_tag 'rtl', :media => 'all' if l(:direction) == 'rtl' %>
    12: <%= javascript_heads %>
    13: <%= heads_for_theme %>
    14: <%= call_hook :view_layouts_base_html_head %>
    15: <!-- page specific tags -->
  app/models/user_preference.rb:39:in `[]'
  app/models/user_preference.rb:57:in `warn_on_leaving_unsaved'
  app/helpers/application_helper.rb:1269:in `javascript_heads'
  app/views/layouts/base.html.erb:12:in `_app_views_layouts_base_html_erb__3203342435659453842_70347210145360'
  lib/redmine/sudo_mode.rb:63:in `sudo_mode'

I don't have an idea, where the problem could be or where i should search, for a solution. Maybe you can help me.
In my old Installation, i use a different theme, but i copied it also to public/themes.

When i first saw my redmine installation in the browser, beofer logging in, the theme was classic. I don't now, where this theme information is saved, i would switch to classic, if that is the soulution.

Thanks for your help and your hints.

Greetings from Germany
Malte