This happened to me a few years ago on a DXB-JFK flight (A345).

We were about 10-15 seconds into the roll when the brakes were applied. The captain announced that the flight attendants should 'emergency positions', but then announced to stand down a few seconds later.

We returned to stand, and were delayed for about 2 hours while they blasted the brakes with cold air.

I really thought the flight was going to be cancelled, I'd have lost my op-up to J

Cheers,
Rick