Redmine

I'm trying to install redmine-0.8.7

I'm getting following error:

[root@c8 redmine_rby]# rake generate_session_store
(in /var/websites/redmine_rby)
rake aborted!
no such file to load -- test/unit/error
/var/websites/redmine_rby/Rakefile:10:in `require'
(See full trace by running task with --trace)
[root@c8 redmine_rby]#

Does anyone know what I'm doing wrong? Is there any file missing under /test/unit/ ??

Following files are there under /test/unit/:

[root@c8 unit]# ls
activity_test.rb journal_test.rb repository_test.rb
attachment_test.rb lib role_test.rb
auth_source_ldap_test.rb mailer_test.rb search_test.rb
board_test.rb mail_handler_test.rb setting_test.rb
calendar_test.rb member_test.rb subversion_adapter_test.rb
changeset_test.rb mercurial_adapter_test.rb time_entry_test.rb
comment_test.rb message_test.rb token_test.rb
custom_field_test.rb news_test.rb tracker_test.rb
custom_value_test.rb project_test.rb user_preference_test.rb
default_data_test.rb query_test.rb user_test.rb
document_test.rb repository_bazaar_test.rb version_test.rb
enumeration_test.rb repository_cvs_test.rb watcher_test.rb
filesystem_adapter_test.rb repository_darcs_test.rb wiki_content_test.rb
helpers repository_filesystem_test.rb wiki_page_test.rb
issue_category_test.rb repository_git_test.rb wiki_redirect_test.rb
issue_status_test.rb repository_mercurial_test.rb wiki_test.rb
issue_test.rb repository_subversion_test.rb
[root@c8 unit]#

Thanks in advance.