MOTU has found that this can be a problem with OSX "disk permissions." To correct it, follow these steps.

1) Boot from your OSX CD (put your CD in computer and while holding down the letter C , restart the computer
2) Once it boots, look on your screen for "disk 1st aid"
click this and choose REPAIR PERMISSIONS
3) Once this command has finished, restart the computer normally and try installing your keycode again.