I was lucky enough to experience the same exact thing on my 147 Selespeed on the first drive out of the dealership. 2 minutes after driving out, I saw VDC failure and ABS failure light come on.
At the dealership 5 minutes later, the Service Manager hooked up the Analysis probe to the vehicle and declared the problem was due to switch connected to the brake pedal.
At that time he asked if I normally drive with my left foot on the brake. I said no, and so they changed the brake sensor switch for a new one.
I have had the car for almost 3 months now, and on Friday, the same thing happened again, except this time it was accompanied with Selespeed failure as well, even though I had no problems chnaging gears.
I took the car again to the dealership, where they diagnosed the same brake switch. The Service manager informed me that it was a common fault on the 147 and a service bulliten was sent out by Alfa Romeo. He told me that all that was needed was adjustment of the switch so that the computer system would detect the brakes applied at a greater distance of the brake pedal travel.
All is fine now and with the fault, there was really no danger of the vehicle becoming dangerous to drive.
For peace of mind, go to the dealer and get the problem diagnosed.