Will Not Shift Into Reverse
 

I am relatively new to the Boxster area. I am an aircooled 911 guy. My son and I have bought a Spec Boxster racer. We are getting it sorted and he is really enjoying the car. At the track last weekend, the car would not shift into reverse. All the forward gears are fine. Is there an interlock of some sort that could be causing this problem? Any suggestions would be appreciated. Thanks,

Tom