Gemfile

source 'https://rubygems.org'

gem 'rails', '3.2.8'
gem 'sqlite3'

# Gems used only for assets and not required
# in production environments by default.
group :assets do
  gem 'sass-rails',   '~> 3.2.3'
  gem 'coffee-rails', '~> 3.2.1'

  # See https://github.com/sstephenson/execjs#readme for more supported runtimes
  # gem 'therubyracer', :platforms => :ruby

  gem 'uglifier', '>= 1.0.3'
end

gem 'jquery-rails'

# Use unicorn as the app server
# gem 'unicorn'

# Deploy with Capistrano
# gem 'capistrano'

gem 'spree', github: 'spree/spree', branch: '1-2-stable'

gistfile1.txt

rails g
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/x86_64-darwin12.0.0/psych.bundle: warning: already initialized constant ANY
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/x86_64-darwin12.0.0/psych.bundle: warning: already initialized constant UTF8
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/x86_64-darwin12.0.0/psych.bundle: warning: already initialized constant UTF16LE
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/x86_64-darwin12.0.0/psych.bundle: warning: already initialized constant UTF16BE
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/stream.rb:12: warning: already initialized constant ANY
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/stream.rb:15: warning: already initialized constant UTF8
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/stream.rb:18: warning: already initialized constant UTF16LE
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/stream.rb:21: warning: already initialized constant UTF16BE
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/sequence.rb:42: warning: already initialized constant ANY
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/sequence.rb:45: warning: already initialized constant BLOCK
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/sequence.rb:48: warning: already initialized constant FLOW
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/scalar.rb:9: warning: already initialized constant ANY
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/scalar.rb:12: warning: already initialized constant PLAIN
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/scalar.rb:15: warning: already initialized constant SINGLE_QUOTED
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/scalar.rb:18: warning: already initialized constant DOUBLE_QUOTED
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/scalar.rb:21: warning: already initialized constant LITERAL
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/scalar.rb:24: warning: already initialized constant FOLDED
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/mapping.rb:16: warning: already initialized constant ANY
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/mapping.rb:19: warning: already initialized constant BLOCK
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/nodes/mapping.rb:22: warning: already initialized constant FLOW
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/visitors/visitor.rb:10: warning: already initialized constant DISPATCH
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/scalar_scanner.rb:8: warning: already initialized constant TIME
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/scalar_scanner.rb:11: warning: already initialized constant FLOAT
/Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/parser.rb:33:in `<class:Parser>': superclass mismatch for class Mark (TypeError)
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/parser.rb:32:in `<module:Psych>'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych/parser.rb:1:in `<top (required)>'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych.rb:7:in `require'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/psych.rb:7:in `<top (required)>'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activesupport-3.2.8/lib/active_support/ordered_hash.rb:2:in `require'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activesupport-3.2.8/lib/active_support/ordered_hash.rb:2:in `<top (required)>'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activesupport-3.2.8/lib/active_support/ordered_options.rb:1:in `require'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/activesupport-3.2.8/lib/active_support/ordered_options.rb:1:in `<top (required)>'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/configuration.rb:2:in `require'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/configuration.rb:2:in `<top (required)>'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/railtie.rb:2:in `require'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/railtie.rb:2:in `<top (required)>'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/engine.rb:1:in `require'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/engine.rb:1:in `<top (required)>'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/plugin.rb:1:in `require'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/plugin.rb:1:in `<top (required)>'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/application.rb:3:in `require'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/application.rb:3:in `<top (required)>'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails.rb:10:in `require'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails.rb:10:in `<top (required)>'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/all.rb:1:in `require'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/all.rb:1:in `<top (required)>'
	from /Users/johanbruning/Documents/Development/store/config/application.rb:3:in `require'
	from /Users/johanbruning/Documents/Development/store/config/application.rb:3:in `<top (required)>'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/commands.rb:24:in `require'
	from /Users/johanbruning/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/railties-3.2.8/lib/rails/commands.rb:24:in `<top (required)>'
	from script/rails:6:in `require'
	from script/rails:6:in `<main>'

Apparently uninstalling "psych" fixed everything.