rails_admin error

gistfile1.txt

           -  Hello, RailsAdmin installer will help you set things up!
           -  I need to work with Devise, let's look at a few things first:
           -  Checking for a current installation of devise...
           -  Found it!
           -  Looks like you've already installed it, good!
           ?  Where do you want to mount rails_admin? Press <enter> for [admin] > 
        gsub  config/routes.rb
       route  mount RailsAdmin::Engine => '/admin', :as => 'rails_admin'
           -  And you already set it up, good! We just need to know about your user model name...
           -  We found 'user' (should be one of 'user', 'admin', etc.)
           ?  Correct Devise model name if needed. Press <enter> for [user] > 
           -  Ok, Devise looks already set up with user model name 'user':
           -  Now you'll need an initializer...
      create  config/initializers/rails_admin.rb
/Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/pry-exception_explorer-0.2.3/lib/pry-exception_explorer/core_ext.rb:76:in `raise': uninitialized constant User::SentActivity (NameError)
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/activerecord-3.2.9/lib/active_record/inheritance.rb:111:in `compute_type'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/activerecord-3.2.9/lib/active_record/reflection.rb:172:in `klass'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/rails_admin-0.4.0/lib/rails_admin/adapters/active_record.rb:257:in `association_model_lookup'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/rails_admin-0.4.0/lib/rails_admin/adapters/active_record.rb:70:in `block (2 levels) in associations'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/rails_admin-0.4.0/lib/rails_admin/config/fields/association.rb:63:in `call'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/rails_admin-0.4.0/lib/rails_admin/config/fields/association.rb:63:in `associated_model_config'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/rails_admin-0.4.0/lib/rails_admin/config/fields/association.rb:33:in `block in <class:Association>'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/rails_admin-0.4.0/lib/rails_admin/config/configurable.rb:68:in `instance_eval'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/rails_admin-0.4.0/lib/rails_admin/config/configurable.rb:68:in `block in register_instance_option'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/rails_admin-0.4.0/lib/rails_admin/config/configurable.rb:42:in `block in register_instance_option'
  from (erb):65:in `block (2 levels) in template'
  from (erb):64:in `map'
  from (erb):64:in `block in template'
  from (erb):53:in `map'
  from (erb):53:in `template'
  from /Users/user/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/erb.rb:838:in `eval'
  from /Users/user/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/erb.rb:838:in `result'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/actions/file_manipulation.rb:111:in `block in template'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/actions/create_file.rb:54:in `call'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/actions/create_file.rb:54:in `render'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/actions/create_file.rb:63:in `block (2 levels) in invoke!'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/actions/create_file.rb:63:in `open'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/actions/create_file.rb:63:in `block in invoke!'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/actions/empty_directory.rb:133:in `call'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/actions/empty_directory.rb:133:in `invoke_with_conflict_check'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/actions/create_file.rb:61:in `invoke!'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/actions.rb:95:in `action'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/actions/create_file.rb:26:in `create_file'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/actions/file_manipulation.rb:110:in `template'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/rails_admin-0.4.0/lib/generators/rails_admin/install_generator.rb:63:in `install'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/task.rb:27:in `run'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/invocation.rb:120:in `invoke_task'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/invocation.rb:126:in `block in invoke_all'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/invocation.rb:126:in `each'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/invocation.rb:126:in `map'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/invocation.rb:126:in `invoke_all'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/group.rb:238:in `dispatch'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/thor-0.16.0/lib/thor/base.rb:425:in `start'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/railties-3.2.9/lib/rails/generators.rb:171:in `invoke'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/railties-3.2.9/lib/rails/commands/generate.rb:12:in `<top (required)>'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/activesupport-3.2.9/lib/active_support/dependencies.rb:251:in `require'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/activesupport-3.2.9/lib/active_support/dependencies.rb:251:in `block in require'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/activesupport-3.2.9/lib/active_support/dependencies.rb:236:in `load_dependency'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/activesupport-3.2.9/lib/active_support/dependencies.rb:251:in `require'
  from /Users/user/.rvm/gems/ruby-1.9.3-p0@project/gems/railties-3.2.9/lib/rails/commands.rb:29:in `<top (required)>'
  from script/rails:6:in `require'
  from script/rails:6:in `<main>'