vba打印问题，求救

mianduhe

下面的程序仅能进行第一次循环，第二次就出现问题，请高手指出问题所在
谢谢！！！
思路：前提先要打开一个dwg文件，然后查找并打印文件架中的其他dwg文件
Public Sub my_batchplotdwg()
   
    Dim plot As AcadPlot
    Dim i As Integer
    Set plot = ThisDrawing.plot
    filepath = ThisDrawing.Path
    fileName = ThisDrawing.Name
    filepathname = filepath & "\" & fileName
    strFileName = Dir(filepath & "\" & "*.dwg", vbDirectory)
    i = 0
    Do While strFileName <> ""
        If i > 0 Then
        Documents.Open (filepath & "\" & strFileName)
        End If
        If ThisDrawing.Active = False Then
            ThisDrawing.Activate
        End If
        ' 验证活动空间是模型空间
        If ThisDrawing.ActiveSpace = acPaperSpace Then
            ThisDrawing.MSpace = True
            ThisDrawing.ActiveSpace = acModelSpace
        End If
        '前后台打印设置
        ThisDrawing.SetVariable "BACKGROUNDPLOT", 0
        ' 设置打印区域的范围和比例、旋转、笔指定
        ThisDrawing.ModelSpace.Layout.PlotType = acExtents
        ThisDrawing.ModelSpace.Layout.PlotRotation = ac0degrees
        ThisDrawing.ModelSpace.Layout.PaperUnits = acMillimeters
   
        '设置打印比例为缩放到图纸大小，并居中打印
        ThisDrawing.ModelSpace.Layout.StandardScale = acScaleToFit
        ThisDrawing.ModelSpace.Layout.CenterPlot = True
        '设置笔为单色
        ThisDrawing.ModelSpace.Layout.StyleSheet = "black.ctb"
        '选择打印机和纸张
        ThisDrawing.ModelSpace.Layout.ConfigName = "TOSHIBA e-STUDIO280Series PCL6"
        ThisDrawing.ModelSpace.Layout.CanonicalMediaName = "A4"
        ' 设置打印份数为1
        ThisDrawing.plot.NumberOfCopies = 1
        ' 设置安静打印
        ThisDrawing.plot.QuietErrorMode = True
        '下一文件
        strFileName = Dir
        '打印
        plot.PlotToDevice
        '关闭文件
        ThisDrawing.Close savechanges:=False
        i = i + 1
        Loop
        '前后台打印设置
        ThisDrawing.SetVariable "BACKGROUNDPLOT", 2
End Sub

 

第一次循环的第一张图可以顺利打印
第二次循环在在执行plottodevice时就会出错
请高手明示
如图：

 

3xxx

好好学习一下。