Passenger could not call the application process

Question

I am deploying my rails3 application on apache2 + passengerv4.0.5 I encountered this problem,

[ 2013-07-03 10:35:00.0181 21203/7f77bb3e6700 Pool2/Spawner.h:739 ]: [App 22245 stdout] [ 2013-07-03 10:36:29.9064 21203/7f77bb3e6700 Pool2/Implementation.cpp:774 ]: Could not spawn process for group /home/ubuntu/plotwatt/alfredo-deploy/current#default: An error occurred while starting up the preloader: it did not write a startup response in time. in 'void Passenger::ApplicationPool2::SmartSpawner::throwPreloaderSpawnException(const string&, Passenger::SpawnException::ErrorKind, Passenger::ApplicationPool2::Spawner::BackgroundIOCapturerPtr&, const DebugDirPtr&)' (SmartSpawner.h:150) in 'std::string Passenger::ApplicationPool2::SmartSpawner::negotiatePreloaderStartup(Passenger::ApplicationPool2::SmartSpawner::StartupDetails&)' (SmartSpawner.h:558) in 'void Passenger::ApplicationPool2::SmartSpawner::startPreloader()' (SmartSpawner.h:206) in 'virtual Passenger::ApplicationPool2::ProcessPtr Passenger::ApplicationPool2::SmartSpawner::spawn(const Passenger::ApplicationPool2::Options&)' (SmartSpawner.h:744) in 'void Passenger::ApplicationPool2::Group::spawnThreadRealMain(const SpawnerPtr&, const Passenger::ApplicationPool2::Options&, unsigned int)' (Implementation.cpp:707) [ 2013-07-03 10:36:29.9070 21203/7f77b8ca1700 agents/HelperAgent/RequestHandler.h:1885 ]: [Client 20] Cannot checkout session. An error occurred while starting up the preloader: it did not write a startup response in time. 

Any idea why this is happening?

For some reason, the application process is not created.