Blizzard Europe has posted a new downloader/installer that everyone on the European Server, who has downloaded the English or German versions of the game, needs to grab. This is not necessary if you pre-downloaded the US version, or any EU version other than German and English, but you MUST get it if you’re using the EU US/DE client. Or you will not be able to play the game.
See the update for the EU and DE versions, for Mac and PC. As the update says, download the installer, put it in the same folder that you ran the 7.6g download/install in previously, and it’s a small and quick update. It took me about 30 seconds to DL and install this whole update.
As Blizzard recommended earlier this week, they strongly suggest that you download the client in advance, especially if you’re going with the digital purchase, since the bandwidth will be quite bottlenecked come launch night. If you haven’t done it yet, now is a good time.