WindBot console pops up and I get error message. Plz help

Hello,

I got some kind of error message;
Couldn't find item named ''.
Everytime I open my bp setup.. Why is

I use

local mainbp = getlootingdestination('mainbp')
local suppbp = getlootingdestination('suppbp')
local lootbp = getlootingdestination('lootbp')
local goldbp = getlootingdestination('goldbp')

closewindows()
openitem(0, 'back')
wait(500,1000)
resizewindows(0, '0')
wait(500,1000)
openitem(suppbp, mainbp, true)
wait(500,1000)
resizewindows(0, '1')
wait(500,1000)
openitem(lootbp, mainbp, true)
wait(500,1000)
resizewindows(0, '2')
wait(500,1000)
openitem(goldbp, mainbp, true)
wait(500,1000)
resizewindows(0, '3')
wait(500,1000)


Thx!