在这个定义的宏中获取错误91？

Question

我在使用自定义功能定义范围时遇到麻烦。这是主要宏：

'1 Selección del archivo de nóminas

    Dim nominas_wb As Workbook
    Dim nominas_path As Variant
        nominas_path = Application.GetOpenFilename(Title:="Seleccione el archivo de nóminas que desee añadir al repositorio:")
            
    If nominas_path <> False Then
        Set nominas_wb = Workbooks.Open(nominas_path)
    ElseIf nominas_path = False Then
        Exit Sub
    End If
    
    Dim nominas_ws As Worksheet
    Set nominas_ws = nominas_wb.Worksheets(1)
    
'2 Definiendo las dimensiones del archivo de nóminas
  
    Dim nominas_range As Range
    nominas_range = nominas_ws.Range(Cells(1, 1), Cells(last_row_index(nominas_ws, 5), last_column_index(nominas_ws, 1)))

...和以下是函数：

Function last_row_index(target_worksheet As Worksheet, target_column_index As Long) As Long

    last_row_index = target_worksheet.Cells(Rows.Count, target_column_index).End(xlUp).Row
    
End Function


Function last_column_index(target_worksheet As Worksheet, target_row_index As Long) As Long

    last_column_index = target_worksheet.Cells(target_row_index, Columns.Count).End(xlToLeft).Column
    
End Function

错误本身是NOMINAS_RANGE = ... line上的错误91。