Blinkers blink fast with the new trailer. Why?

[TowX]

Way back in '07 when I got my previous open deck trailer, the blinkers would blink fast, and all the trailer lights would flash every 10 seconds or when the truck was turned off. Dealer recoded it and everything worked just fine. And even a couple of rented uHaul trailers worked fine too.

Now with the new enclosed trailer, I have the same old problem back again. Blinkers blink fast, and all the trailer lights flack every 5 seconds or so, even when the X5 is running. I plugged my old trailer in (they're sitting side by side) and everything is normal.

The only difference I can think of is that the enclosed trailer has a lot more clearance lights than the open trailer. And the new trailer has LED blinker/brake lights while the open trailer has traditional dual filament bulbs. I know LED's draw less power and could cause this kind of problem. But if the X5 was coded for towing, why wouldn't it work for all trailers plugged in? I find it nuts that BMW would not make an electrical system for any type of lights.

As a simple check, I grabbed my ex's Explorer which has the factory towing package. Plugged in the open trailer and all works fine. Plugged in the new trailer and all is still fine. So the problem is the X5. My dealer is stumped and suggested that I'd need to recode each time I change trailers, which is not going to happen! And BMW NA was no help either.

Any thoughts or advice??