I've got an m3u file which only has one line (C:\Users\James\Documents\Music). When I load this in Windows Media Player, I get an error saying "the selected file has an extension (.) that is not recognized by Windows Media Player, but the Player may still be able to play it" (it can't). When I try opening it with VLC of FooBar2000, it works fine. How can I get WMP to load the playlist?
It seems that WMP doesn't know how to handle such M3U files, even though they are valid according to the M3U specification. However, you can instead right-click the folder in Explorer and select Play with Windows Media Player.