The scenario is invalid due to a too long name for the .scx file. You can play from the editor, useless for a Multiplayer though.
To play from standard game, random map, and then scenario, rename the .scx with a shorter title in your scenario folder or load the file in the editor, exit the editor, click save as and choose a shorter name.
You can recognize an invalid .scx file in your scenario folder, the KB do not show in the file name and going standard game, random map, scenario only a part of the name displays in the upper box.
@ The author, edit using the update form, I send you an e-mail some days ago.
@ The player, do not download unless you want to go through the procedure above.