I get "Could not find a valid gem 'listen'" although it is installed

Question

I want to install sass 3.3.0.rc.6:

C:\Ruby200>gem install -p http://proxy.*****:8080 sass --pre

Temporarily enhancing PATH to include DevKit...
Building native extensions.  This could take a while...
ERROR:  Error installing sass:
    ERROR: Failed to build gem native extension.

C:/Ruby200/bin/ruby.exe mkrf_conf.rb
C:/Ruby200/lib/ruby/2.0.0/rubygems/dependency_installer.rb:308:in `find_spec_by_name_and_version': Could not find a valid gem 'listen' (< 3.0.0, >= 1.1.0) locally or in a repository (Gem::SpecificGemNotFoundException)
    from C:/Ruby200/lib/ruby/2.0.0/rubygems/dependency_installer.rb:109:in `available_set_for'
    from C:/Ruby200/lib/ruby/2.0.0/rubygems/dependency_installer.rb:329:in `install'
    from mkrf_conf.rb:18:in `<main>'
Ensuring you have the right version of listen installed.
Installing listen >= 1.1.0, < 3.0.0


Gem files will remain installed in C:/Ruby200/lib/ruby/gems/2.0.0/gems/sass-3.3.0.rc.6 for inspection.
Results logged to C:/Ruby200/lib/ruby/gems/2.0.0/gems/sass-3.3.0.rc.6/ext/gem_make.out

So I need listen >= 1.1.0, < 3.0.0...?

The problem is: I arleady have it:

C:\Ruby200>gem list

*** LOCAL GEMS ***

bigdecimal (1.2.0)
celluloid (0.15.2)
celluloid-io (0.15.0)
ffi (1.9.3 x86-mingw32)
io-console (0.4.2)
json (1.7.7)
listen (2.7.0)
minitest (4.3.2)
[...]

Why I'm getting an error?