'ZO_SortHeader_OnMouseEnter' error

[Argusus]

Hello,

i'm getting the message below. i'm trying to mimic the ScrollListExample. my data is displaying but the sort doesn't work. is there any simple things to double check for this error?

EsoUI/Libraries/ZO_SortHeaderGroup/ZO_SortHeaderGroup.lua:264: attempt to index a nil value
stack traceback:
	EsoUI/Libraries/ZO_SortHeaderGroup/ZO_SortHeaderGroup.lua:264: in function 'ZO_SortHeader_OnMouseEnter'
	11557962843809674184:3: in function '(main chunk)'