The website/people are saying you need to use Factorio version 0.18.11 at least, this is partially incorrect. KS2 only works in a range of 0.18.11 - 0.18.15 and will not work on 0.18.6 or higher. You can revert to earlier versions of Factorio on the Steam menu.
You might not realize, but 0.18.6 is actually a lower version than 0.18.11 the way the version numbering system works. At least that is the only way I can determine that your message would make sense. Versions go ..., 0.18.9, 0.18.10, 0.18.11, ...
Ahh yes you're correct, I thought that was weird.
The issue is the way that Steam orders the Beta list. The newest version is placed in the middle of the list, making it counter-intuitive. The versions go in ascending order until the 18.1xxx, and then the 1xx's are in descending order.