If you're using Zend Server, you need to make sure you load xDebug before zend extension manager.
extension_dir="C:\Program Files (x86)\Zend\ZendServer\lib\phpext"
zend_extension="C:\Program Files (x86)\Zend\ZendServer\lib\phpext\php_xdebug.dll"
xdebug.remote_enable=1
xdebug.remote_handler=dbgp
xdebug.remote_mode=req
xdebug.remote_host=127.0.0.1
xdebug.remote_port=9000
zend_extension="C:\Program Files (x86)\Zend\ZendServer\lib\ZendExtensionManager.dll"