Leaderboard problems: FindFirstChild a nil value...????

Hello. So I have a mainscript, and within that a function that looks like this:

function awardcredit(player, credits)
if player and credits then
local leaderstats = player:FindFirstChild("leaderstats") -- line 32 btw
if leaderstats then
local value = leaderstats:FindFirstChild("BlitzCreditz")
if value then
value.Value = value.Value + credits
end
end
end
end

This is supposed to add some credits (A value on the leaderboard. More on that in a moment...) This is where I call this function in the script

awardcredit(activecontestants, 4)

I also have my leaderboard set up like this...

function playeradded(player)
	local leaderstats = Instance.new("Model")
	leaderstats.Name = "leaderstats"
	leaderstats.Parent = player
	
	local points = Instance.new("IntValue")
	points.Name = "Wins"
	points.Parent = leaderstats
	points.Value = 0
	
	local BC = Instance.new("IntValue")
	BC.Name = "BlitzCreditz"
	BC.Parent = leaderstats
	BC.Value = 0
	
	
	
end
game.Players.PlayerAdded:connect(playeradded)
for _, player in pairs(game.Players:GetPlayers()) do
	playeradded(player)
end 

The output says this when I get to the awardcredit(activecontestants, 4) in the script... workspace.MainScript:32: attempt to call method 'FindFirstChild (a nil value) Any idea why?

FindFirstChild

Although I am not exactly sure as to what activecontestants has been initialized as, the error you are getting often is from the mistake of calling FindFirstChild on an array. The FindFirstChild method can only be used on instances. Arrays, although they are technically objects, arrays are not instances. You may be slightly confounded on why I am repeating array again and again, although you haven't initialized an array anywhere. The main reason for this is that I'm assuming [since you haven't shown it] that activecontestants was the product of using GetChildren or GetPlayers on a prior instance

For example:

local activecontestants = game.Players:GetPlayers()
print(activecontestants:FindFirstChild("Player1"))
--Error

Again, the main explanation for this is the fact that using GetChildren or GetPlayers returns an array, which FindFirstChild can NOT be used on.

Using FindFirstChild Properly

The proper way to use FindFirstChild is to use on the instance instead. For example, let's make a script that looks for a player 'Player1' inside the Players service.

local plr = game.Players:FindFirstChild("Player1")
if plr then
print(plr.Name .. " is in the Server!")
end

This is how FindFirstChild should be used. Here is an example of what NOT to do:

local plr = game.Players:GetChildren():FindFirstChild("Player1")
if plr then
print(plr.Name .. " is in the Server!")
end

Fixing The Issue

Using what has been discussed, let's try fixing your code. Again, I'm under the assumption that players and activecontestants are both meant to be arrays.

function awardcredit(activePlayers, credits)
for _,v in pairs(activePlayers) do
  local stats = v:FindFirstChild("leaderstats")
  local blitz = v:FindFirstChild("BlitzCreditz")
   if stats and blitz then
      blitz.Value = blitz.Value + credits
   emd
end

Useful Links

FindFirstChild: http://wiki.roblox.com/index.php?title=API:Class/Instance/FindFirstChild

GetChildren: http://wiki.roblox.com/index.php?title=API:Class/Instance/GetChildren

Instance Type: http://wiki.roblox.com/index.php?title=API:Class/Instance

Handling Arrays: http://wiki.roblox.com/index.php?title=Table#Reading_from_and_writing_to_arrays