The green 2.1's are more thoroughly tested than the previous batches which had the FAT errors. There's nothing really wrong with the design, I think the problem was caused by bad cold soldering. The green 2.1's are basically the same as the original Acekard 2's which didn't have FAT errors -- I have one and it still works fine. They simply undergo better testing to ensure that the soldering is OK.
The black PCB's have been redesigned to eliminate the possibility of the FAT errors. As someone said, they don't have a chip sticking out. In addition, the black PCB's are supposed to use slightly less power (around 20 to 30 minutes according to most sources).
-Bri