Springs? floor tools normally have them as the most important part of hard floor mode or something, or maybe a plastic latch isn't corresponded properly even if it looks like it's right, for example I think you might remember my DC40 has a cog in the yolk, it looked like it would just fit in but it had to have the end correspond to the first hole it goes into for the stabiliser to work right (aswell as thatblack clip I had trouble putting in lol)
Hope it helps