If you're sure you've followed the instructions, used all the correct elements and connect the flow as expected, I'll make the following guess:
Look at the hello,world element in the model, and compare it to the two elements in the following screenshot paying special attention to the icon on left:
Does it look like the top or bottom one. The top one is a constant (which is what you should use), and the bottom is a data element, which looks quiet similar, but will not work in this demo as it does not contain a value.
If that is not the case, I can suggest that you export the application (via File -> Export -> Archive File) and post it to this thread.
For best results, use the Firefox browser..