I have a 1230 also. The second time I used the walking foot (which was so pricey I waited a long time before finally biting the bullet and getting it!) the back of the foot caught on a safety pin I had missed while machine quilting. The foot was ruined. My dh took it apart and told me a spring inside had been damaged; he could fix it if I could get a replacement spring. Unfortunately, Bernina doesn't sell replacement springs (or so the shop told me). I finally bought another walking foot and have been *very* careful with it ever since. (I now spray baste so don't have to worry about safety pins!)
Anyway, the upshot of all this is that the problem is likely to be with the foot, not the machine.
Are you absolutely sure you have installed the walking foot properly? The little fork is surrounding the screw that holds the needle in place? If the foot is installed properly, then my guess is that the foot is damaged in some way.