When I add directories to Foobar's playlist, the actual directory is added to the playlist instead of its contents. If I try to play the resulting playlist item, the following error message appears: The problem occurs regardless of how I add the directory (shell extension, drag & drop, Foobar's menu), but strangely not all the time. Sometimes it's enough to restart Foobar to get it working again, other times nothing seems to help. Even rescanning the media library results in only a few directories in the "?" category, along with the abovementioned error message if I attempt to play them. I use Foobar 0.9.4.5 on Vista x64.

Please see this thread: Reading folders as files

Thanks! I did have the Matroska plugin. Hopefully the problem disappears along with it.