<p>Staring JBoss server from within Eclipse Ganymede gives me the following problem:
"Server JBoss v4.0 at localhost was unable to start within 120 seconds. If the server requires more time, try increasing the timeout in the server editor."</p>

<p>The console shows JBoss has started in so and so minutes but soon after, there is a pop up if the above message.
I can also start the JBoss externally. </p>

You may check whether you are running Jboss version 4.0.4 or version 4.2.2.  You might get this error when you have installed Jboss 4.2.2 but configured Jboss 4.0.4 in Eclipse.