As a CodeWarrior I dislike it when "submit" tests completely hide what is tested and then catch you by surprise as you muddle through failed special case after failed special case -- this often turns what seemed like straight-forward and simple problem into a drawn out and unncessarily complex experience. I also dislike it when a kata has "tricky" tests in the submit-tests but address it by burying the details in in text of the "details" section. My approach to deal with these issues for this Kata was to provide commented approaches with a second comment about the problem with that particular implementation. My approach gives both a hint on what the "submit" tests will enforce while educating on why that approach is bad. edit fixes double-mention about flaw comments

MinBy is an eager LINQ operator -- meaning it immediately determines its result. For another challenge of implementing a different kind of LINQ operator you might try my SelectConsective kata.

Check the docs what are parameters of Enumerable.Range. I also got tripped by this once.

What kind of error?

Your range isn't really correct, try to look at error messages to see why.