Spring MVC - servlet requested source not available

I tried to make a simple web app with Spring MVC and I follow this tutorial from Netbeans:

http://netbeans.org/kb/docs/web/quickstart-webapps-spring.html

And I get the problem: The requested source not available ?

My questions:

1. What is this problem from ?开发者_Go百科 [ I'm quite sure it is from servlet - Tomcat ]
2. How to fix this

Thanks all, I compress the project and run on my friend's laptop. It's fine, maybe there are problems when I run my project. Thanks for all of your effort :)