iTunes crashes on Genius Update

I'm using iTunes 11.0.55 on Windows 8 64 Bit. I have a huge library consisting mostly of lossless DRM-less M4A files. The music is stored on a NAS.

After enabling Genius, while creating the initial Genius database, iTunes always crashes after about 15-20% / 10 minutes.

I tried the following to remedy the problem:

- Do a clean uninstall & new install of iTunes

- Creating a new library

The problem first happened after I (unsuccessfully) tried to share the library with a Macbook notebook. However I recreated and reinstalled iTunes since, so it really can't be the source of the problem.

Thanks for help!

- Johannes