New tyres & mover problem

moulesy

I guess I should know the answer to this but I don't so I'm hoping some bright spark out there does! We've just had brand new tyres fitted to the van. Correct tyres inflated to correct pressure as per handbook. But now I can't get the mover rollers to stay
engaged on the tyres. They move on to the tyres OK (it's a manual version) but I don't get that final click when the rollers should engage. Anyone think of a reason why? Would letting a little air out to decrease the tyre pressure work and would it be safe
anyway? It' s not a problem when we're on site as I can reverse OK but no way can we get the van back in store without the mover. Hope someone has an answer, otherwise it's another, presumably expensive, trip to the dealers!