May 14th, 2012 
Lythknight Well it is now past 8:01am on 5/14/2012, so you should no longer be getting the “unexpected decryption error” when trying to install Diablo 3. However, if you are still getting the unexpected decryption error then you either have corrupted installation files or you need to finish downloading the diablo 3 installation package.
To fix the problem go to where you downloaded your “Diablo-III-8370-enUS-Installer” folder (which is most likely in C:\users\[your computer username]\Diablo-III-8370-enUS-Installer or in C:\Program Files\Diablo-III-8370-enUS-Installer or C:\Program Files(x86)\Diablo-III-8370-enUS-Installer and see if you have any “.part” files there.
If you do then you need to restart your “Diablo-III-8370-enUS-Installer-downloader.exe” file. If you don’t remember where you downloaded the “Diablo-III-8370-enUS-Installer-downloader.exe” file to, but you found your “Diablo-III-8370-enUS-Installer” folder, then just download the diablo 3 installer from battle.net (or below if you are pre-installing without a battle.net preorder) and then when it ask where to save the files, just point it to the “Diablo-III-8370-enUS-Installer” folder again and it will resume the download.
In the worst case senario (corrupted installation files) you just need to re-download the installer (preferrably through battle.net) and re-download all the Diablo 3 Setup Files.
Once the download is complete, the Diablo 3 installer will automatically launch the Diablo 3 game installation and the actual setup will begin.
Windows:
- enGB
- enUS – USA English
- enSG
- German/deDE
- Spanish/esES
- French/frFR
- Italian/itIT
- Polish/plPL
- Taiwan Mandarin
- Korean/koKOR
- Spanish/esMX
- Portuguese/ptBR
MAC
If you downloaded the Diablo 3 Installer prior to May 12th, 2012 and you live in Europe then you need to use the new diablo 3 installers below to be able to download all the diablo 3 files.
New Europe (EU) English Installer
New Europe (EU) English Installer (Mac)
New German Installer
New German Installer (Mac)
This error message generally indicates that the installation files may be corrupted, damaged or incomplete. Please make sure your download has finished before attempting to install the game. Secondly, make sure the installation executable file is in the same folder as all your other Diablo III installation files. If the problem persists, you may need to delete all the files and restart the download.
Your installation folder should not have any files with the .Part extension. If it does, it indicates the downloader was closed prematurely. Restart the downloader in this case, selecting the same location the “Diablo-III-8370-enUS-Installer” folder is in, and it will check the existing files and download what’s missing. It’s important to let the downloader finish on it’s own. It will start the “Diablo III Setup.exe” file when it’s done. It can take a while so please be patient.
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