why do you think the problem is your web.xml descriptor? It's difficult to test without the whole application but the descriptor doesn't look too bad.
You should take a look at the log files for your servlet container or application server for more information what went wrong. As this is a JSF application the problem could be missing JAR files or something totally different, too. But this is hard to tell just from the descriptor and the very short error message. Take a look at the logs!