I followed the chapter 1 of the new byond guide step-by-step and I'm still getting this error code. Everything was fine until I added the login location info of:
loc = locate(/turf/start) GreattFriend-0002/image.png
Chapter 1 of the guide defines /turf/start, which your code does not. Hence the error.

For getting help on the forums, you're better off pasting the code here instead of an image. Be sure to put your code inside of <dm> ... </dm> tags so it's readable.
In response to Lummox JR
I might be misunderstanding some jargon here. My code has mob as the parent, Login() as the proc, and it's defined with the loc = (/turf/start) . That's how the guide shows it (from what I read). I copy/pasted it. Unless for some reason I can't have 2 procs under mob. But it worked when I had multiple things under turf
What Lummox JR means by "defining" /turf/start is that the guide adds a turf called "start" in the second to last code block in chapter 1. Specifically, that code block is:

icon = 'floor.dmi'
start // THIS IS THE /turf/start DEFINITION
icon = 'start.dmi'
icon = 'wall.dmi'
density = 1
icon = 'player.dmi'
loc = locate(/turf/start)

Your code does not have the portion that I've placed a code comment next to.

If you add that portion (in other words, if you define /turf/start in your code), it will compile and execute.