I bought Diablo II online the other day, through the electronic download. I've downloaded the Diablo II Installer, but whenever I start it up it says, "Installation not authorized," and soon after that an error message will pop up and say "There was a problem authenticating your download. Please go to battle.net/account and redownload." I've spoken to the customer service reps at Blizzard multiple times, and they say there's nothing wrong with it on their end, and have even given me tips, such as disabling my firewall and trying to download it in "Safe Mode with networking," to no avail. They assume it has something to do with my computer's security software, and I still don't have my game downloaded. Any and all help would be appreciated.

My computer is a Acer Aspire 5755 running Windows 7 Home Premium. To date, I have:
-uninstalled McAfee Security
-turned off firewalls
-ran computer in Safe Mode with Networking
-ran the computer with Selective Start-up
-deleted and redownloaded multiple times
all with no success.