you didnt do something silly like leave it parked for 3 months with the handbrake on by chance did you?
sounds to me like your rear brakes may well have stuck which will confuse the hell out of the ABS system.
on a normal car the front brakes probably do about 90% of the work as all the weight and drive is at the front wheels thats were the vast majority of the braking is done, the brakes are on the rear wheels usually only for handbrake and to stop the car spinning when you do brake.
make sure the brake fluid level is topped up and give the brakes a good hammering, if the brake discs are particularly rusty, although be careful as braking efficiency will be reduced. see if it goes away in a few days. if it doesnt have to look harder.
oh and also make sure the battery is well charged, failure to do so can do strange things to alfas.