Could not find compatible versions for gem "activemodel" on bundle update rails

Question

I broke my application trying to update to rails 4 and now do not know what to do, can someone please help - thank you! What can I do to just get all my gems back to the versions they should be?

my error:

C:\sites\code\OM Rails\omrails>bundle update rails
  Fetching gem metadata from https://rubygems.org/........
  Fetching gem metadata from https://rubygems.org/..
  Resolving dependencies...
  Bundler could not find compatible versions for gem "activemodel":
    In Gemfile:
      simple_form (>= 0) x86-mingw32 depends on
          activemodel (~> 3.0) x86-mingw32

      rails (= 4.0.0.rc1) x86-mingw32 depends on
          activemodel (4.0.0.rc1)

gemfile:

source 'https://rubygems.org'

gem "activerecord"
gem 'rails' , '4.0.0.rc1'
gem "jquery-rails"
gem "devise" 
gem 'simple_form'
gem "paperclip"
gem 'aws-sdk'
gem 'will_paginate' 
gem 'bootstrap-will_paginate'
gem 'thumbs_up'
gem 'activeadmin'
gem "meta_search"    
gem 'acts-as-taggable-on'
gem 'postmark-rails'
gem "railties"

group :production do
  gem 'pg'
end

group :development, :test do
  gem 'sqlite3'
end

group :assets do
  gem 'sass-rails', '4.0.0.rc1'
  gem 'coffee-rails', '4.0.0'
  gem 'bootstrap-sass', '~> 2.3.2.1'
  gem 'uglifier', '>= 1.0.3'
end

gem "mocha", :group => :test

Answer 1

Try removing gem "activerecord" from your Gemfile

The rails 4 gem should install the version of ActiveRecord that it wants as one of its dependencies