edit the "invalid answer" look and feel

I have been struggling with making this work, even following the video in jeanie's post. It was working and has now stopped!

I have found another solution; you can disable a custom submit button (we were using a custom one anyway) and only enable it when you click on a response. This would ensure that the user has made a choice, as they cannot un-tick a box. The invalid answer screen will not show at all in this case, so it doesn't have to be edited. 

The only draw back with a custom submit button is hotspots don't work that well, and the storyline view turns into a horizontal nightmare!!!!