Lua Error w Mining Turtle w repeat loops

I am trying to run the following code (which I don't see what is wrong with it):

print("Mine by Guard13007 (adv version of excavate that mines through anything)")
print("Pattern is right and and forward from current position.")
print()
write("Enter width: ")
sW = io.read()
nW = tonumber(sW)
print()
write("Enter length: ")
sL = io.read()
nL = tonumber(sL)
print()
write("Enter height: ")
sH = io.read()
nH = tonumber(sH)

z = 1
-- z is height up and down nH
repeat
print("Level "..z)
z=z+1

y = 1
-- y is width left to right nW
repeat
  print("Line "..y)
  y=y+1

  x = 1
  -- x is length front to back nL
  repeat
   x=x+1
   turtle.digDown()
   turtle.forward()
  until x >= nL

  test=y%2
  if test==1 then
   turtle.turnRight()
   turtle.forward()
   turtle.turnRight()
  else
   turtle.turnLeft()
   turtle.forward()
   turtle.turnLeft()
  end
until y >= nW

turtle.down()
if test==1 then
  --turn right and go back to start using width and turn right
  turtle.turnRight()
  y = 1
  repeat
   y=y+1
   turtle.forward()
  until y >= nW
  turtle.turnRight()
else
  --turn left and go back using width, turn left, use length to go back to start, turn left, turn left
  turtle.turnLeft()
  y = 1
  repeat
   y=y+1
   turtle.forward()
  until y >= nW
  turtle.turnLeft()
  x = 1
  repeat
   x=x+1
   turtle.forward()
  until x >= nL
  turtle.turnLeft()
  turtle.turnLeft()
end

until z >= nH

--go up
z = 1
repeat
z=z+1
turtle.up()
until z >= nH

print("Mining complete.")
exit()

I get this error when trying to run it:

[attachment=225:2012-05-15_14.54.07.png]

What's wrong?

An even better solution, can someone explain how to use the while loop? I can't seem to get it to work.

while i >= 5 do
i=i+5
--other stuff
end

That sort of thing always returns "expected "do"" I've tried with >= and => and > and none work (is it limited to == and ~=? that seems stupid to me if that is the problem, so that can't be the problem).

The code seems to be ok, except for the exit() call at the end, there's no such function. It might be a typo in your code, did you copy this from the file or by hand?
The while syntax is correct, it would never end since you add 5 and check if it's higher than 5, but the syntax it's ok. Again, it might be a typo.