After hours of pain in my head, I found the solution:
http://redmine.ruby-lang.org/issues/show/4300I reinstalled my ruby environment and that was the reason, why rubygems was updated to 1.5.0. Rubygems 1.5.0 changes the yaml parsing default from syck to psych and psych doesn't like the ":<<" in yaml files.
Add this to the beginning of your config/environment.rb, if you have libyaml installed (default with rvm ruby 1.9.2):
require 'yaml'
YAML::ENGINE.yamler= 'syck'
Now, everything works fine.
Regards,
sewid