This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Classes get an automatic no arg constructor only if you don't create any constructors. That's why your class will compile when you uncomment the line with super() in it. The reason why it's a compile-time error is that it has no way of compiling the subclass without calling the parent class.
Another way of expressing it: This is one of those things the javac tool can recognise as a problem. So it prevents you from getting into trouble by not allowing the problem beyond the compiling stage.
You should be able to find out about constructors in any decent Java book.