Humanoid Ai Problems?

First of all, Players = game.Players:GetChildren() saves a table to Players which your repeat until loop will indefinetly check if it stops existing later in the script.

Second of all, function Vardoesn't return. Try the following:

-- Also I renamed it to be more descriptive of what it actually does
local function getDist(p1,p2) return (p1.Maginitude - p2.Maginitude).Maginitude end

Third of all, line 11 is in no the correct way of calling a function. Try the following syntax:

local distance = getDist(human.Torso, v.Character)

Also, human = workspace.Humanoid won't work because Humanoid needs to be inside a character of some sort in order to run a WalkTo command.

Line 15, you called function Repeat() before it exists.

On line 22, human.Humanoidis the same thing as (substitute human for the variable declaration at the beginning of script) workspace.Humanoid.Humanoid

There is nothing correct about this script. But I will get you started in the right direction:

local diff = 0
local comp = 0
local human = workspace.Character
local Humanoid = human.Humanoid
local Target

local function getDist(p1,p2) return (p1.Maginitude - p2.Maginitude).Maginitude end

spawn(function() -- spawn runs a function on a separate thread
	while true do
		if Target then
			human.Humanoid.WalkToPoint = Target
			wait()
		end
	end
end)

function getTarget()
	for i,v in pairs(game.Players:GetPlayers()) do
	    if Target == nil and 100 > getDist(human.Torso.Position , v.Character.Torso.CFrame.p) then
	    	-- If the distance between the NPC Torso and the Character is less than 100
	        Target = v.Character.Torso.CFrame.p
	    end
	end
	wait(1)
	getTarget()
end

Not guaranteeing the script I gave you is worth anything, but good luck anyway.