symfony: Composer insallation methods fails

I’m trying to install the latest version of Symfony with the Composer methods, but when I type php composer.phar create-project symfony/framework-standard-edition Symfony 2.1.7, I get this :

Installing symfony/framework-standard-edition (v2.1.7)

    Installing symfony/framework-standard-edition (v2.1.7) Downloading: 100%

Created project in Symfony
Loading composer repositories with package information
Installing dependencies from lock file

    Installing jdorn/sql-formatter (v1.2.0)
    Loading from cache

   [...]

    Installing symfony/swiftmailer-bundle (v2.1.7)
    Loading from cache

    Installing twig/extensions (dev-master 5c2d515)
    Cloning 5c2d515d4624bdd588226d688173cf0399a4d8cf

kriswallsmith/assetic suggests installing leafo/lessphp (Assetic provides the in
tegration with the lessphp LESS compiler)
kriswallsmith/assetic suggests installing leafo/scssphp (Assetic provides the in
tegration with the scssphp SCSS compiler)
kriswallsmith/assetic suggests installing ptachoire/cssembed (Assetic provides t
he integration with phpcssembed to embed data uris)
kriswallsmith/assetic suggests installing leafo/scssphp-compass (Assetic provide
s the integration with the SCSS compass plugin)
monolog/monolog suggests installing mlehner/gelf-php (Allow sending log messages
to a GrayLog2 server)
monolog/monolog suggests installing ext-amqp (Allow sending log messages to an A
MQP server (1.0+ required))
monolog/monolog suggests installing ext-mongo (Allow sending log messages to a M
ongoDB server)
Generating autoload files
PHP Warning: require_once(app/autoload.php): failed to open stream: No such fil
e or directory in C:\wamp\www\Symfony\vendor\sensio\distribution-bundle\Sensio\B
undle\DistributionBundle\Resources\bin\build_bootstrap.php on line 24
PHP Stack trace:
PHP 1. {main}() C:\wamp\www\Symfony\vendor\sensio\distribution-bundle\Sensio\B
undle\DistributionBundle\Resources\bin\build_bootstrap.php:0
PHP Fatal error: require_once(): Failed opening required 'app/autoload.php' (in
clude_path='.;C:\php\pear') in C:\wamp\www\Symfony\vendor\sensio\distribution-bu
ndle\Sensio\Bundle\DistributionBundle\Resources\bin\build_bootstrap.php on line
24
PHP Stack trace:
PHP 1. {main}() C:\wamp\www\Symfony\vendor\sensio\distribution-bundle\Sensio\B
undle\DistributionBundle\Resources\bin\build_bootstrap.php:0

Warning: require_once(app/autoload.php): failed to open stream: No such file or
directory in C:\wamp\www\Symfony\vendor\sensio\distribution-bundle\Sensio\Bundle
\DistributionBundle\Resources\bin\build_bootstrap.php on line 24

Call Stack:
0.0010 632720 1. {main}() C:\wamp\www\Symfony\vendor\sensio\distributi
on-bundle\Sensio\Bundle\DistributionBundle\Resources\bin\build_bootstrap.php:0

Fatal error: require_once(): Failed opening required 'app/autoload.php' (include
_path='.;C:\php\pear') in C:\wamp\www\Symfony\vendor\sensio\distribution-bundle\
Sensio\Bundle\DistributionBundle\Resources\bin\build_bootstrap.php on line 24

Call Stack:
0.0010 632720 1. {main}() C:\wamp\www\Symfony\vendor\sensio\distributi
on-bundle\Sensio\Bundle\DistributionBundle\Resources\bin\build_bootstrap.php:0

Script Sensio\Bundle\DistributionBundle\Composer\ScriptHandler::buildBootstrap h
andling the post-install-cmd event terminated with an exception

[RuntimeException]
An error occurred when generating the bootstrap file.

create-project [-s|--stability="..."] [--prefer-source] [--prefer-dist] [--repos
itory-url="..."] [--dev] [--no-custom-installers] [--no-scripts] [--no-progress]
[--keep-vcs] package [directory] [version]

I don’t know whether this has to do with Composer or Symfony standard edition…