You sould try to clean the sensors on your ABS. They will crud up and give a false error message.
Cleaning them is fairly easy. For the front pull the wheel. The sensor is located on the top of the spindle. You can follow the wires going to it to locate it. The wiring connector plugs strait down onto the sensor - there is not a holding tab on the connector and it is a snug fit. Once the connectoe is off you can remove the retaining screw. The sensor can be pulled up to remove. It is a sealed unit and the grime and metal filings can be wiped off. The rear is simular.
Go to Matthew's main page for a good list of how-to's for the brakes and other issues for enlightenment.