Mob Farm Code Error

I am trying to create a code for an advanced monitor that I can click to change the active mob in a MFR auto-spawner. I am trying to automate this with a peripheral proxy but the basic selection part of the code I can not seem to get working. I want to just click the menu at the top then the mob, but when I try to click the menu the error: mobfarm:57: attempt to compare nil with number occurs. I greatly appreciate any help that is given! Thank you!

Code (I couldn't get the paste function to work): Pastebin at BSdryL92

Picture: Pastebin at ZmZS5kqT.

Please and thank you!

lua is case sensitive.

while true do
local event, button, x, y = os.pullEventRaw() --#lowercase x, y
  if slc == 0 then
    if event == "mouse_click" then
      if X >=2 and X <=8 and Y ==1 and button ==1 then --#uppercase X, Y
      drawMenu1()
      slc = 1
        else
        drawDesktop()
      end
    end
   elseif slc == 1 then
     if X >=1 and X <=11 and button ==1 and Y==3 then slc = 0 --#uppercase X, Y
       os.reboot()
       else
       slc = 0
       drawDesktop()

     end
  end
end

Oh my gosh! Thank you so much!!! It is working perfectly now! On a side note, if I were to make all the coordinates lowercase would that work, as long as they are consistent? Or do they have to be uppercase for lua no matter what?

It doesn't matter whether they're uppercase or not, so long as they're consistent.

Thank you! I'll be sure to remember this in the future.