Downloading world: do [ /dl world {name} ], text should pop up on screen saying "Compressing world", than "Creating download link", followed by a link to download a zip file, if you still have issues with it, provide no name and only use a name if you are downloading another world than the main world. Downloading a Schematic: first of all, make sure you have edit, than do //wand to get a worldedit wand, and select the parameters of the schematic you want to download, then just do [ /dl schematic {name} ], should work just the same!
If either of these do not work try the following: Re logging, Restarting the server, and Force stopping and Starting the server.