Probably a sensor, probably a wheel speed sensor issue (or harness sending the signal to the ABS/TDC ecu). Before the ABS/TDC was able to detect it was getting a bad signal, it was using that signal as a real signal. So say you are traveling at 60mph, and it thinks a wheel, or all wheels are at 0kph, it will cut the brakes completely. In this case, the fail safe detection should happen quickly enough that it doesn't cause a huge issue. This is why we do, or should do, extensive FEMA/FTA testing, but as we all know, not all systems or cars are created equal. The good thing is, if the ABS/TDC light is solid on, it's detected them problem and the system shouldn't intervene now. The other good thing is, there is a code in the system for whatever sensor the system is getting a bogus signal from. Unfortunately since it's not the FI ecu, you can't just hook up a generic code reader to it. You will need someone with a maker specific capable (ABS) code reader. Someone with an expensive Snapon/etc, or a dealer will easily be able to pull up the code.
Baring that, one of the first things I would check is looking in the wheel wells to see if there is an obvious disconnected connector or damaged harness for the wheel speed sensors. Being down in the wheel well, they are more likely to get damaged over time.