I had this problems in Ruby 1.8.7-p374.
When try to run "rake db:migrate" i got this error:
RubyGems installed the following executables:
/home/wellington/.rbenv/versions/1.8.7-p374/bin/gem
RubyGems system software updated
/home/wellington/.rbenv/versions/1.8.7-p374/bin/rake:22: undefined method `activate_bin_path' for Gem:Module (NoMethodError)
Its occurs on deploy Rails apps.
Any ideas to solve this?