[symfony-users] Task generate-admin is not defined.

hai I m trying to run this command php symfony propel:generate-admin backend RoomBooking -- module=home for my backend application for admin generator where RoomBooking is my propel object. when i run this command i get the Error Task generate-admin is not defined. i dont know whats the

[symfony-users] Task generate-admin is not defined.

when I run this command in terminal [Fedora 7] php symfony propel:generate-admin backend answer i got following error Task generate-admin is not defined. I was just doing as it is mentioned in the website but with a different database { answer is a table in my database}