Can you navigate to this location:
IO error: C:\Users\Internet\AppData\Roaming\Bitcoin\chainstate\713704.ldb: Zugriff verweigert (access denied)
from the command line?
The IO error and access denied messages would seem to indicate that it can not access those directories, so you should try and see if they are accessible.
Also, as long as I am asking, what version? (probably not relevant, but who knows).
Yes, I'm able to navigate. I use the latest client on W7 64bit with all updates. In the meantime the client closed after over an hour with high cpu load. I always run the client as no root. Maybe it is an general access problem, I had another problem to write a file to an USB-stick, but not reproduceable.
How can it happen, that I'm able to access a directory and a moment later it doesn't work? That's crazy.