Looks like the Worksheet_Change() sub needs two edits:
Dim defRange As Range ' Without this statement, defRange is a variant type, not a range
And add a Set statement to defRange =:
Set defRange = ActiveWorkbook.Sheets(“LookUpTable”).Range(“WISKILookupTable”)
Hence, the defRange variable now refers to the actual range. If not, the values in that range are used for defRange, which is not what you want.
Also, it's generally a good idea to include an Option Explicit declaration on the module's initial line. That will alert Excel to problems involving variable types and will detect the Set statement that is missing.
You will be forced to Dim every variable by Option Explicit, but that's also best practice.