C# Windows Media Player how to Delete a Playist (WMPLib.IWMPPlaylist)

Question

I'm trying to delete a WMPLib.IWMPPlaylist in C# I've already tried it with these methods

WMP.playlistCollection.remove(playlist);
WMP.playlistCollection.setDeleted(playlist, true);

as well as this code from a similar question:

IWMPPlaylistArray plCollection = WMP.playlistCollection.getByName("myplaylist");
if (plCollection.count > 0)
{
    IWMPPlaylist pl = plCollection.Item(0);
    WMP.playlistCollection.remove(pl);
}

but I didn't get it to work. The playist is the current playlist of the windows media player. I hope you guys can help me out.