I am running Symfony 2.0.6, and I get the following error:
InvalidArgumentException: There is no extension able to load the configuration for "knp_menu" (in /home/www/Symfony/app/config/config.yml). Looked for namespace "knp_menu"
It works in DEV, but not in PROD enviroment.
The error message means that you got an entry "knp_menu" in your config.yml which is not used by any extension.
It's either a caching problem (you introduced the extension, e.g. a bundle, and then not cleared the prod cache), or you load a specific bundle only within the dev environment (as the profiler in a default symfony2 app).
Try clearing the cache using php app/console clear:cache --env=prod --no-debug
. If the problem exists anyhow, find out which bundle uses knp_menu and either delete the configuration or enable the bundle.