Missing list subscript for ISELEMENT argument: <list name>

You called the IsElement function and did not include the list tag, which is required. For example:

Dim myList List As Double
myList("Alex") = 12345
myList("Martin") = 23456
If IsElement(myList) = TRUE Then Print "Yes."              ' Illegal
If IsElement(myList("Mary")) = TRUE Then Print "Yes."      ' Legal

Specify a list tag when you call IsElement.