trouble with dig turtle program

Anyone knows what this error means?
mine:33: attempt to compare __lt on nil and nil

function that gets the error
"if x > nx then" is line 33 in my code

Spoiler

–Detect which direction turtle is facing
function getF()
local fac = "0"
local x,y,z = gps.locate(1,false)
refuel()
turtle.forward(1)
local nx,ny,nz = gps.locate(1,false)
turtle.back(1)
if x > nx then
fac = "1" –East
elseif x < nx then
fac = "3" –West
elseif z > nz then
fac = "2" –South
elseif z < nz then
fac = "0" –North
else
print("Position didn't change. Something blocking turtle?")
fac = "Error"
end
return fac
end

My entire code is here:
http://pastebin.com/aWwfcRSr

I know what's wrong, the gps api for gps.locate is returning nil because it couldn't get replies from gps host computers because you forgot to turn on a rednet modem.

Yeah just figured it out.
Wireless transmitter on the turtle was off.

Adding rednet.open("right") fixed it.

But for some reason turtle.dig() isn't doing anything.
Can a normal turtle not dig dirt?

Edit: Mining Turtle seems to be working the way I want it.
Except I put it bit too close to my house now, lol.

if it's a mining wireless turtle it can, but if it's a regular wireless turtle(with no tool on it), it can't dig at all.

Guys i'm getting the same error. with line 64 it's: if xTarget > xCoord then
look("west")
PS: I'm not using a wireless one.

Your variables are nil. Make sure they're actually being assigned a value, and in scope if they're locals.

Can't provide much more help without more code.

What do you mean by "nil" sorry, kinda new to computercraft.

From the lua manual:

Nil is the type of the value nil, whose main property is to be different from any other value; usually it represents the absence of a useful value.

Here's the code please let me know if you know what it is.
http://pastebin.com/EFFvY6vM

xTarget and zTarget haven't been declared at that point in the code.

Also you have at line 37: function.moveUp() should be function moveup()
And you have an infinite loop in moveDown()

Fixed all the problems except the __lt, i meant line 66 (64 in computercraft).

Can you please help me?