运行时错误'1004' - 工作簿受保护

Question

我编写了这段代码，用于将工作表从一个工作簿移动到另一个工作簿。它一直工作到昨天，突然投掷

Run time error '1004': Workbook is protected and cannot be changed

以下是代码。 Debug显示END SUB之前的最后一个语句是问题。我无法弄清楚什么是错的。

Sub copydata()
    Dim wkbSource As Workbook
    Dim wkbDest As Workbook
    Dim shttocopy As Worksheet
    Dim wbname As String

    ' check if the file is open (source file)
    ret = Isworkbookopen("C:\Users\Desktop\Scorecard\Write Offs.xlsx")
    If ret = False Then
        ' open file
        Set wkbSource = Workbooks.Open("C:\Users\Desktop\Scorecard\Write Offs.xlsx")
    Else
        Set wkbSource = Workbooks("Write Offs.xlsx")
    End If

    ' check if the file is open

    ret = Isworkbookopen("C:\Users\Desktop\Scorecard\Copy data from one excel to another.xlsm")
    If ret = False Then
        ' open file
        Set wkbDest = Workbooks.Open("C:\Users\Desktop\Scorecard\Copy data from one excel to another.xlsm")
    Else
        Set wkbDest = Workbooks("Copy data from one excel to another.xlsm")
    End If

    'Sheet to be copied from the PEH write off report
    Set shttocopy = wkbSource.Sheets("PEH WBB TOTAL MPG")
    shttocopy.Copy wkbDest.Sheets(1)
End Sub