java.lang.illegalstatexception Application was not properly initialized

I am getting the following error when deploying an application on JBoss 4.2.1

   7:05:59,673 ERROR [Application Name]StandardWrapper.Throwable
   jav开发者_JAVA百科a.lang.IllegalStateException: Application was not properly initialized at 
   startup, could not find Factory: javax.faces.context.FacesContextFactory

I browsed the net and I found many posts which suggested to add an entry in web.xml but that entry was already there. And all the required libraries are there in web-inf.

So any solutions anybody ?

Ensure that your classpath is clean (i.e. no duplicate different versioned classes/JAR files, keep in mind that JBoss ships with builtin JSF libraries!) and that your web.xml is declared as at least Servlet 2.3.