这段简单的用来合并文件的vba代码，一运行就报自动化（automation）错误，怎么解决呢？

Sub wjhb()
Dim str As String
Dim wb As Workbook

str = Dir("d:\data\*.xls*")

For i = 1 To 20
    Set wb = Workbooks.Open("d:\data\" & str)
    
    wb.Sheets(1).Copy after:=ThisWorkbook.Sheets(ThisWorkbook.Sheets.Count)
    ThisWorkbook.Sheets(ThisWorkbook.Sheets.Count).Name = Split(wb.Name, ".")(0)
    
    wb.Close
    str = Dir
    If str = "" Then
        Exit For
    End If
Next
End Sub