Chitty is correct, there was something amiss with the fuel tanks and the aircraft couldn't carry enough fuel to get to Nantes. Dublin was in its range and of course once there it got the required maintainance. Obviously Ryanair Ops should've been aware but these things happen. And yes righthandrule, Jet2 are just as bad, changing LIRFs last minute and not informing the baggage lads in time causing delays and not to mention your very own secret aircraft changes that no-one outside Jet2 Ops knows about...