iTunes-cover screensaver not showing

Today I tried to use the iTunes-cover screensaver (for the first time), but my screen (and the preview area in the system preferences) simply stays black, nothing else happens.

Has anybody experienced this too or has an idea what to do?

Try the following:

• Restarting iTunes
• Restarting the Mac
• Quitting iTunes and relaunching it while holding down the ⌥ key (to designate a different library), then quitting and relaunching it and re-pointing it at your real library
• Selecting a completely different screensaver, then reselecting the iTunes Artwork screensaver.
• Repair disk permissions