It seems this is a problem with the Early 2011 Unibody's. The best, fastest and most reliable SanDisk-cards can't be read from those new machines. That is so frustrating.
My iMac from January and an 13" Unibody from last year have no issues with those cards whatsoever.
I have a 15" i7 MBP and am facing the same issue with two cards - the SanDisk Extreme Pro 16GB and the Extreme HD Video 16GB.
This is nothing short of a huge FAIL on Apple's part. I am really disappointed.
I just upgraded my camera gear to have SD-cards with me, but now I can still continue carrying the external card-reader. This is painful.
However, my hope is, that this can be amended by a driver update.
But only if the problem is recognized within the big corperation in Cupertino.
So, please! Call the support hotline and have them FILE A RADAR, so a ticket can be opened. Eventually, someone will have to look at this and fix it!
Same issue:
https://discussions.apple.com/thread/3034444