Ahh I just had to wait. It took 45 minutes - but now it started without problems and synced.
Thank you anyways
You should update to 0.12 regardless. On windows systems anti virus software can often find signatures of viruses in the blockchain data. The software will then lock the files, which will cause the bitcoin client to crash. There is a fix that comes with 0.12 as it stores the data obfuscated so the virus signatures (there are actually some in the blockchain, but they cant harm you) do not get detected.