Brakes Towing - Ever had this happen?

[CTDCAL]

Towing my 30' fiver for the first time, using a prodigy controller, everything works fine, good brakes on trailer, truck working perfect. On a windy slow going paved road, taking it easy on the brakes, letting the engine and gears do the work, occassional light taps on the brakes to keep RPM's where I'm happy (no e-brake yet, but soon!). I hear the ding, then the ABS warning light comes on and the then the red brake warning light. Stop and check everything, nothing hot, brake fluid where it should be, trailer brakes work, truck brakes work. I continue on as I was only 5 miles from our destination. Figure the warning lights would reset after a little while or after I cycle the ignition. Still on! start manuvering to set up the trailer and presto, the lights go out and stay out. Stayed for 5 days and just came home over the same road without any problems and lights did not come on again.

Anyone have any idea what caused this????? 60k on the truck, a few mods to the engine, but nothing too radical. I have towed alot with this truck, much of it more weight than the fiver, but this is the first time off the fifth wheel hitch, all gooseneck and tounge trailers before.

Any feedback would be appreciated.