I was struggling to get an application to deploy in Eclipse the other day. The exception I was getting is shown below. The reason this exception warrent inclusion on this site is simply because there wasn't actually anything wrong with my applicaiton. In order to clear this exception I stopped Tomcat and deleted the working folder for the application that was causing me touble. I'm not quite sure why this worked but I think it is because of some serialized state that gets placed in the context by the faces servlet so that it knows everything has been started. When Tomcat is shutdown this state is serialized out. Upon restart it gets brought back in and under some situations it looks like it can confuse the application.

java.lang.IllegalStateException: No Factories configured for this Application - 

typically this is because a context listener is not setup in your web.xml.
A typical config looks like this;
org.apache.myfaces.webapp.StartupServletContextListener
javax.faces.FactoryFinder.getFactory(FactoryFinder.java:101)
javax.faces.webapp.FacesServlet.init(FacesServlet.java:88)
org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:691)
org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:658)