Invalid spell slot in GetSpellCooldown

[Twisted6]

Running the macro on Turtle WoW 1.18:
/run if not buffed("Clearcasting") then Channel("Arcane Missiles(Rank 1)") else Channel("Arcane Missiles") end

I get the error SM_Slash.lua:563: Invalid spell slot in GetSpellCooldown

[Monteo]

Low rank Arcane Explosion, max rank if Clearcasting

/run SpellStopCasting() local i,x=1,0 while UnitBuff("player",i) do if UnitBuff("player",i)=="Interface\Icons\Spell_Shadow_ManaBurn" then x=1 end i=i+1 end if x==1 then CastSpellByName("Arcane Explosion")else CastSpellByName("Arcane Explosion(Rank 1)")end

[Monteo]

/script local q; local t;for i=0,15,1 do t=GetPlayerBuffTexture(i); if (t and string.find(t, "ManaBurn")) then q=1; break; end; end; if(q ~= nil) then CastSpellByName("Arcane Missiles(Rank 7)") else CastSpellByName("Arcane Missiles(Rank 1)"); end;