Getting issue when clicking the drop-down buttons to reset a spell.

Error occured in: Global
Count: 1
Message: Interface/SharedXML/UIDropDownMenu.lua line 91:
calling 'GetWindow' on bad self (Usage: local window = self:GetWindow())
Debug:
[string "=[C]"]: ?
[string "=[C]"]: GetWindow()
[string "@Interface/SharedXML/UIDropDownMenu.lua"]:91: UIDropDownMenu_Initialize()
[string "@Interface/SharedXML/UIDropDownMenu.lua"]:1167:
Interface/SharedXML/UIDropDownMenu.lua:1024
[string "=[C]"]: ?
[string "=[C]"]: ?
[string "=[C]"]: ToggleDropDownMenu()
[string "@Interface/AddOns/Critline/Libs/Libra/Dropdown.lua"]:80: Toggle()
[string "@Interface/AddOns/Critline/SpellList.lua"]:58:
Interface/AddOns/Critline/SpellList.lua:53
Locals:
(*temporary) = defined =[C]:-1

The same thing happens to me. Here is my error message.

2x SharedXML/UIDropDownMenu.lua:91: calling 'GetWindow' on bad self (Usage: local window = self:GetWindow())
[string "=[C]"]: in function GetWindow' [string "@SharedXML/UIDropDownMenu.lua"]:91: in function UIDropDownMenu_Initialize'
[string "@SharedXML/UIDropDownMenu.lua"]:1167: in function <SharedXML/UIDropDownMenu.lua:1024>
[string "=[C]"]: ?
[string "=[C]"]: ?
[string "=[C]"]: ?
[string "=[C]"]: ?
[string "=[C]"]: in function ToggleDropDownMenu' [string "@Critline/Libs/Libra/Dropdown.lua"]:80: in function Toggle'
[string "@Critline/SpellList.lua"]:58: in function <Critline/SpellList.lua:53>

Locals:
(*temporary) =

{
menuList = {
}
_displayMode = "MENU"
initialize = defined @Critline/SpellList.lua:17
xOffset = 0
SetHeight = defined @Critline/Libs/Libra/Dropdown.lua:27
yOffset = 0
}