that was actually my first guess too .
but nothing is blocking it i checked like 10 times , i have 2 hud ,first one is player health which is shown on top left , second one is hotkey bar on lower right .
the created hud in runtime are all images and not buttons .
I even created another GUI Layer , and put it at the top , and assigned my skillbar hud to it. but it is still not clickable.
Actually control maps work . i assingned "1" key to first spell , "2" key to second , and when i press 1 or 2 , they work , so it is something with the hud .