転記元の最終行を取得するところで1004エラーがでる

Dim fl As String
Dim WBo, Wbd As Workbook
Dim a As String
Dim ex As String
Dim syamei As String

Sub 変換ファイル選択()
syamei = Range("B3")
fl = Application.GetOpenFilename
ThisWorkbook.Worksheets(1).Range("C1") = fl
Set WBo = Workbooks.Open(fl)
MsgBox "出力先を選択"

With Application.FileDialog(msoFileDialogFolderPicker)
.Show
a = .SelectedItems(1)
End With
With ThisWorkbook.Worksheets(1)
ex = a & "\" & .Range("B3") & "_" & Year(Now) & "_" & Month(Now) & ".xlsx"
.Range("C2") = ex
.Activate
End With
Set Wbd = Workbooks.Add
Wbd.SaveAs ex
ThisWorkbook.Worksheets(2).Activate
ActiveSheet.Copy Wbd.Worksheets(1)
ThisWorkbook.Worksheets(1).Activate
End Sub