Redmine

I am trying to install redmine in a SL6.4 machine 64 bit.
I've followed some general guides like https://www.redmine.org/projects/redmine/wiki/Redmine+Apache+Passenger_InstallOnRedHat but the first problem is here

[root@heplnv152 redmine]# RAILS_ENV=production rake db:migrate                                                                                                                                                                               
rake aborted!                                                                                                                                                                                                                                
NameError: uninitialized constant Rails::Initializer                                                                                                                                                                                         
/redmine/config/environment.rb:35:in `<top (required)>'                                                                                                                                                                                      
Tasks: TOP => db:migrate => environment                                                                                                                                                                                                      
(See full trace by running task with --trace) 

I get the same problems with several different redmine versions.

Any help would be really appreciated. Thanks.