When i did my CBT pre DAS a while back, hadnt been on a bike in many years, i had brilliant instructors, they created a great rapport almost imediately and that helped the day go. Whilst i passed 2 other guys failed, one couldnt get the hang of the clutch and the other was really poor in all aspects, despite the school actually giving the other 2 guys 1 to 1 instruction for an hour whilst i was patient. When i went onto DAS one of the failed guys was on that too but he just couldnt get the hang of the bigger bikes either. I think its a lot like that, nerves can get the better of you, and this directly translates into really poor performance because you are constantly on edge. Or you just arent suited to bikes. I think you'll be fine with the right instructor. The right instructors are key.