Using WMP12 with DLNA

I'm trying to use Windows 7 / WMP12 with DLNA. But I'm stuck in turning on
media sharing. When ever I click the button "Turn on media streaming" it goes
gray and the donut appears for half a second. Then nothing else happens.
Media sharing remains off and and no error message appear. Neither have I
found anything in the eventlog.

I noticed other people mentioning the same problem. But no solution.

Anyone who knows this problem and how to fix it?

TIA,
Jan