LISTTAG argument is not a FORALL alias variable

You used an invalid argument when you called the ListTag function. The ListTag function may only be passed the ForAll reference variable of the ForAll statement:

Dim Y List As String
ForAll X In Y
   Print ListTag(ABC) ' Illegal
   Print ListTag(X)   ' Legal
End ForAll

Replace the invalid argument in the ListTag function call with the ForAll reference variable where ListTag appears.