将键传递给函数作为字符串参数时，VBA Excel错误“按参考参数类型不匹配”

我在以下子test（）上收到“按引用参数类型不匹配”错误：

Public Function GetOtherDict(k As String, dict As Dictionary) As Dictionary

    Dim otherDict As New Dictionary

    curItem = dict.Item(k)
    otherDict.Add curItem, curItem

    Set GetOtherDict = otherDict
End Function

Public Sub Test()

    Dim dict As New Dictionary
    dict.Add "a", 1
    dict.Add "b", 2

    For Each k In dict.Keys

        Dim otherDict As Dictionary
        Dim curKey As String
        curKey = k 
        Set otherDict = GetOtherDict(k, dict)

    Next

End Sub

当我GetOtherDict用curKey参数而不是参数调用函数时，k错误消失了。

您能告诉我为什么需要这个多余的声明吗？