VESA mount difficulty with 30" CD

Hi

I've just come into a barely used 30" Cinema Display for my FCP system, but need to wall mount it for some space and clearance issues. I've got the

Apple VESA adaptor and a Bretford wallmount arm.

But, when I follow the directions for removing the monitor's stand -- with the little credit card piece of plastic to be inserted in a slot above the stand -- I swear there is no slot. I have the monitor tilted all the way forward and yet there is not a visible slot or space that this card will go into. Yes, there's a "seam" but it doesn't open up even the few millimeters it might take to slide in the card.

Any guess as to what I'm doing wrong? Is it possible that the 30" is different than other models in this regard?

Any thoughts?

My thanks in advance.