Graded Question slides progressing with incorrect answer - not using question bank

I have a storyline with questions to be answered that is for whatever reason, progressing to the next slide, even when answered incorrectly. I am the 2nd person to look at this and have compared it against other, working storylines and everything seems correct. 

the ONLY way i have been able to force it to stay on the slide is to add in a trigger to jump to the current slide at start of the "try again" layer... this of course makes the "try again" layer flash on the screen and go away. 

I'm sure its something I've missed as we're still pretty new to articulate. 
I have attached a copy of the story file.

Much appreciated in advance