Possibilities:
1. If you're now using the temporary spare wheel this is a normal situation and the ABS light will go off when the normal sized wheel and tyre is refitted.
2. If a new tyre has been fitted and the size is different to the others then this will cause the problem.
3. When the rear of the car was jacked up to change the wheel the wiring to the ABS sensor may have been damaged.
Bingo, September 2007