as noted from blizzard's blog
Quote from: http://eu.battle.net/d3/en/blog/4410912/
We became aware of an issue affecting the previously available German and EU English versions of the digital install downloader for Diablo III, which would not download all the necessary files. If you've pre-downloaded the digital version of the game in these languages before 10:00 AM CEST (9:00 AM GMT) on Saturday May 12, you must obtain the new downloaders to be able to install properly once the game is released on May 15. We apologize for the inconvenience, and ask that you please let friends and acquaintances know so they can begin downloading the working installer that's now available.
1. Obtain the new Diablo III digital downloader using the links below
2. Point the download save at the same directory as before
The folder in question is your main game data folder. If you have the game downloaded to D:\Games\Diablo-III-8370-enGB-Installer, please point the download to D:\Games\. Do not use the automatically generated folder containing the installation files (i.e. do not use the directory D:\Games\Diablo-III-8370-enGB-Installer as this is the one created by the downloader).
3. If you chose the correct directory only around 65MB will need to be downloaded to fix your install, otherwise you'll re-download the entire ~7.6GB
New EU English Installer
New EU English Installer (Mac)
New German Installer
New German Installer (Mac)
For more information or help with the installation, check out the Diablo III Pre-Sale Downloader Walkthrough or use the search on the Battle.net support site.
Whether you repair your previous install or download the entire game again, it's necessary to use this new downloader to install and play the game when it launches.