Lua math error?

if x2<x1 then
   x3=x2
   x4=x1
  else
   x3=x1
   x4=x2
end
if y2<y1 then
  y3=y2
  y4=y1
else
  y3=y1
  y4=y2
end
if z2<z1 then
  z3=z2
  z4=z1
else
  z3=z1
  z4=z2
end

for x=x3,x4 do
  for y=y3,y4 do
   for z=z3,z4 do

tArgs={...}
username=tostring(tArgs[1])
x1=tArgs[2]
y1=tArgs[3]
z1=tArgs[4]
x2=tArgs[5]
y2=tArgs[6]
z2=tArgs[7]
block=tArgs[8]
meta=tArgs[9]
count=0
iterations=0
p=peripheral.wrap("right")
pl=p.getPlayerByName(username)
w=p.getWorld(p.getPeripheralWorldID())
if x1~=nil and x2~=nil and y1~=nil and y2~=nil and z1~=nil and z2~=nil then
if x2<x1 then
   x3=x2
   x4=x1
  else
   x3=x1
   x4=x2
end
if y2<y1 then
  y3=y2
  y4=y1
else
  y3=y1
  y4=y2
end
if z2<z1 then
  z3=z2
  z4=z1
else
  z3=z1
  z4=z2
end
print("x: "..x3.." - "..x4)
print("y: "..y3.." - "..y4)
print("z: "..z3.." - "..z4)
for x=x3,x4 do
  for y=y3,y4 do
   for z=z3,z4 do
	count=count+1
	iterations=iterations+1
	if count>=10000 then
	 count=0
	 sleep(0.05)
	end
	w.setBlockWithoutNotify(x,y,z,tonumber(block),tonumber(meta))
	if iterations==1 then
	 pl.sendChat("Setting blocks...")
	end
   end
  end
end
end
if iterations==0 then
pl.sendChat("For loop not executed.")
end
pl.sendChat(iterations.." blocks changed in "..math.floor(iterations/10000).." seconds.")