Function error?

Hi.i want to create a file with some improved functions, to make the creation of apps or operative system more easier.
That is my problem.
When i call the my function:

form.createTitleBar("[Menu]",1,1,32,128)

, i've get this error:

window:57:excepted number
Press any key to continue

After 5 seconds my pc will be shutdown if i don't press any key.
This append only with the form.createTitleBar() function not with other
There is the function:

function form.createTitleBar(Testo,X,Y,ColoreSfondo,ColoreTesto)
local w,h = term.getSize()
term.setCursorPos(1,Y)
term.setTextColor(Sfondo)
term.setBackgroundColor(Sfondo)
term.clearLine()
for V=0,w,1 do
  term.setCursorPos(V,Y)
  write(".")
end
term.setTextColor(ColoreTesto)
term.setCursorPos(X,Y)
write(Testo)
end

Where is the problem?

well, when you defined the function you used colorSfondo. if you later want to use that variable, you cant use sFondo, you have to use colorSfondo