I had this very same problem and tech support could not help me even after multiple installs. I have a macbook pro with the latest snow software. i'm not mac wiz but in browsing my computer for hours there is a file with express invoice or similar in the computer hidden in wich you need to delete and then reinstall, maby a preference file?. (it is a file that does not get removed uninstalling) after deleting that it worked flawlessly after reinstall. make sure you saved a backup to reload after your fix.