Can't get a question slide to work with keypresses...

Hi all,

I have this problem with a question slide that I am developing. This does not go to a results screen etc. If you look at the example you have a choice of 4 answers, you choose one by clicking on it with your mouse and then click the Submit button. By the way 450 is the right answer! And you get feedback layers with these silver grey oblong panels telling you if you are right or wrong. This all works OK when you use your mouse BUT...

I want this to work just with keypresses for accessibility reasons if someone cannot use a mouse. If you click the icon in the top-right hand corner it shows you which key to press, for example, you can choose an answer by pressing one of the following keys; 1, 2, 3, 4 and after you have picked one you press the T key to submit.

Now... this doesn't work even after I have selected the correct answer as a get this white box stating "Invalid answer" which is not in one of my feedback layers. See the image.

Do these types of questions work with keypresses or am I actually doing something wrong?

Thanks in advance.

Keith