I`ve found a small bug while searching for some of my old templates in singleplayer-mode. I found the tutorial scenario and decided to try it.
The first message I got was: This template has only 1 slot please remove the other players.
So I deleted the other three AI`s but then I got the message that I should play with at least 2 players. So you can`t play that scenario unless you change it. It is not a big bug nor very important, but I thought I should just say it.

You're right - the tutorial template isn't usable by itself. The only way to play the tutorial is via the Tutorial button at the top of the single-player main page. Thanks for reporting it.