I thought that I would 'upgrade' my halo bulbs (they are originals and the car is now 12 years old!) So I bought a pair of LED bulbs
BMW X5 E53 White 5-LED Xenon Bright ICE Side Light Beam Bulbs Pair Upgrade | eBay from the bay of flees. They turned up and the bayonet fitting was off centre meaning I had to sand one of the nodules down in order to fit. Once done, I installed into the car, bulb works, side indicator stays on and the car still says 'Check Park Lights'. So... there must be a resistor that I would have to wire into the system. Anyone have any ideas? To be honest, for the time it would take me I might just get the cheap units from ebay in China. I have seen that they do a W5 for under £10 now.