Redmine needs a functional instance of ruby on rails with gem version 1.3.7
You can check your gem version by using this command:
If you have a superior version than 1.3.7, the steps necessary in order to downgrade your gem version are below:
Go to your preferred work directory (ex. /usr/local/src)
tar xzvf rubygems-1.3.7.tgz
Afterwards, check your gem version:
And this should return:
After these operations, all gems need to be reinstalled in order for them to work properly.