I am Damien Pendleton, the author of the audio_form class.
I have had a brief look at your code, and from what I can see, there must have been a bug in the class provided in version 1.0. I have done a lot of bug fixing of the form class over the time taken to revise the BGT engine.
To give you an idea, the window must be created first in the form before any further controls can be created. So if you have created your controls before the window, you will have no returned ID's because there is no window to create them on.
I'm not exactly sure how your game should work - I have tried to test various things and since there are hardly any comments or structure to the code I can't get a quick grasp of what is meant to happen when the game is launched. However, my theory is that if you move the window creation code up to before where you create the controls, the form should work as expected for you.
If it doesn't, come back to me and I will work with you to do some extensive testing with it.
Hope this helps.