DVD region reset problem

I changed my DVD region code to watch a region 1 (due to a bad delivery from Amazon), knowing that I had one change left. When I tried to change back to region 2, I get the correct dialogue box telling me I can change back, but that this is the last allowed change of region (as expected). I unlock, enter my admin password and everything looks fine. When I click the 'Set Drive Region' button, the drive region menu box closes and I'm back to square one, with no change to the region....I can do this any number of times, and it's the same...I have a region 2 disk in the machine and I have tried restarting. How can I solve this dilema.

This is on a Macbook pro with Intel core 2 duo.

At least on my iMac, the free and widely-respected media player VLC is unaffected by region codes and is at least as a good a player of DVD as the DVD player app that comes with the machine.