ich fand dies hier:

Found the source of the problem with the latest 9.1 update on Windows 7. There problem is with the Bonjour update - if you disable Bonjour, the rest of iTunes will be happy again.

Disabling Bonjour means you won't be able to use AppleTV or AirTunes, but everything else works.

You can either uninstall Bonjour, or just stop it when you run iTunes.

To stop Bonjour running, click Control+Alt+Del and go to Task Manager. Choose 'processes' and click 'show processes for all users'. Bonjour should now appear in the list. Right-click on it and choose 'stop'.

You'll then be able to launch iTunes. It will give you a message about Bonjour being disabled, but you can ignore that.

Hopefully Apple will fix the problem soon. It seems to be something to do with the way Windows 7 handles user accounts, in that Bonjour doesn't seemed to be linked to the account you're using.


edit: gerade bei Itunes empfielt es sich nicht jedes update mitzumachen, diese sind oft fehlerhaft.