Adding APC to Symfony project causes Fatal Error

Adding APC to Symfony project causes Fatal Error

Very new to Symfony so apologies if the answer is obvious. I am trying to
add APC to a project to see if it improves performance. I am running
symfony with easyphp on Windows 7/Windows 8 (installed on usb). APC is
installed in ext folder and added to php.ini file as:
extension=php_apc.dll
then at end of file:
[APC]
apc.enabled = 1
apc.shm_segments = 1
apc.shm_size = 128M
apc.max_file_size = 5M
apc.stat = 1
php works fine with these settings. However when I now try to load my
Symfony project I get the following error:
FatalErrorException: Compile Error: Cannot redeclare class
Doctrine\Common\Persistence\Mapping\Driver\MappingDriverChain in
F:\EasyPHP\data\localweb\projects\SymfonyProj\vendor\doctrine\common\lib\Doctrine\Common\Persistence\Mapping\Driver\MappingDriverChain.php
line 36
Not sure if I have my caching set up all wrong or I am missing some config
options somewhere?