This is not a taint, since the error message say the "listFrame" doesn't existed, so according to the code line
Lua Code:
local listFrame = _G["DropDownList"..level];
The ui drop down menu provided by the blz has only two levels, limited by "UIDROPDOWNMENU_MAXLEVELS". So if you want use more levels, the error will be raised. I don't check the 3rd libs, according to the page, if you use NoTaint UIDropDownMenu, you may change the LIB_UIDROPDOWNMENU_MAXLEVELS to a more big value.
If you still have problem, I also have a lib for drop down menu, you can search
ShowDropDownMenu in
https://github.com/kurapica/Scorpio/.../004.widget.md