Could not open input file: app/check.php al haber instalado Symfony2 y ejecutado el "app/check.php" para comprobar si se ha instalado correctamente.

Hay que situarse correctamente en el directorio donde está instalado Symfony2 para poder hacer el check. Una vez situado en el directorio probad de nuevo y veréis que os sale algo parecido a esto:

********************************
* *
* Symfony requirements check *
* *
********************************

* Configuration file used by PHP: C:\xampp\php\php.ini

** ATTENTION **
* The PHP CLI can use a different php.ini file
* than the one used with your web server.
* (especially on the Windows platform)
* To be on the safe side, please also launch the requirements check
* from your web server using the web/config.php script.

** Mandatory requirements **

OK PHP version must be at least 5.3.3 (5.3.8 installed)
OK PHP version must not be 5.3.16 as Symfony won't work properly with it
OK Vendor libraries must be installed
OK app/cache/ or var/cache/ directory must be writable
OK app/logs/ or var/logs/ directory must be writable
OK date.timezone setting must be set
OK Configured default timezone "Europe/Berlin" must be supported by your
installation of PHP
OK json_encode() must be available
OK session_start() must be available
OK ctype_alpha() must be available
OK token_get_all() must be available
OK simplexml_import_dom() must be available
OK detect_unicode must be disabled in php.ini
OK PCRE extension must be available

** Optional recommendations **

OK Requirements file should be up-to-date
OK You should use at least PHP 5.3.4 due to PHP bug #52083 in earlier ver
sions
OK When using annotations you should have at least PHP 5.3.8 due to PHP b
ug #55156
OK You should not use PHP 5.4.0 due to the PHP bug #61453
WARNING When using the logout handler from the Symfony Security Component, you
should have at least PHP 5.4.11 due to PHP bug #63379 (as a workaround, you can
also set invalidate_session to false in the security logout handler configurati
on)
Install PHP 5.4.11 or newer if your project uses the logout handler fr
om the Symfony Security Component.

WARNING You should use PHP 5.3.18+ or PHP 5.4.8+ to always get nice error mess
ages for fatal errors in the development environment due to PHP bug #61767/#6090
9
Install PHP 5.3.18+ or PHP 5.4.8+ if you want nice error messages for
all fatal errors in the development environment.

OK PCRE extension should be at least version 8.0 (8.12 installed)
OK PHP-XML module should be installed
OK mb_strlen() should be available
OK iconv() should be available
OK utf8_decode() should be available
OK filter_var() should be available
WARNING intl extension should be available
Install and enable the intl extension (used for validators).

WARNING a PHP accelerator should be installed
Install and/or enable a PHP accelerator (highly recommended).

WARNING realpath_cache_size should be above 1024 in php.ini
Set "realpath_cache_size" to e.g. "1024" in php.ini* to improve perfor
mance on windows.

WARNING short_open_tag should be disabled in php.ini
Set short_open_tag to off in php.ini*.

OK magic_quotes_gpc should be disabled in php.ini
OK register_globals should be disabled in php.ini
OK session.auto_start should be disabled in php.ini
OK PDO should be installed
OK PDO should have some drivers installed (currently available: mysql, od
bc, sqlite, sqlite2)