So here is the deal. You try to log in to the store to download and you get an error. DO NOT create a new username, reboot your system, change your password, etc. The error is simply due to network traffic.
DO just keep trying to log in. You will get there. It may take 10 plus tries but all you have to do is get the error, go back, click it again, after a few tries you will get in. You may get this error on some of the screens when you are in as well. Simply hit the back button and try again, it will work after a few attempts.
After selecting your game simply go to account management -> Transaction Management -> Services List -> SCEA Promotions and there you click the link to download your free games.
Again if any of the screens gives you the error hit your "O" button to go back and click it again.