ThumbnailCtrl shadow

Can someone tell me why I am getting this error, when I run
the program below. I have the ThumbnailCtrl.py in the same
directory. If I comment out

         t, b, s = getShadow()
         self.shadow = wx.MemoryDC()
         self.shadow.SelectObject(s)
and
         if not thumb._alpha:
             dc.Blit(imgRect.x+5, imgRect.y+5, imgRect.width, imgRect.height, self.shadow, 500-ww, 500-hh)
in ThumbnailCtrl.py, then it runs but no of course no shadow.
Thanks
Phil

Traceback (most recent call last):
   File "E:\r09\py\tnc\ThumbnailSimple.py", line 35, in <module>
     frame = ThumbnailSimple().Show()
   File "E:\r09\py\tnc\ThumbnailSimple.py", line 10, in __init__
     self.TC = TC.ThumbnailCtrl(self.panel, -1)
   File "E:\r09\py\tnc\ThumbnailCtrl.py", line 556, in __init__
     thumbfilter=thumbfilter)
   File "E:\r09\py\tnc\ThumbnailCtrl.py", line 722, in __init__
     t, b, s = getShadow()
   File "E:\r09\py\tnc\ThumbnailCtrl.py", line 195, in getShadow
     return (sh_tr, sh_bl, sh_sh.ConvertToBitmap())
   File "C:\Python25\Lib\site-packages\wx-2.8-msw-unicode\wx\_core.py", line 3336
, in ConvertToBitmap
     return _core_.Image_ConvertToBitmap(*args, **kwargs)
wx._core.PyAssertionError: C++ assertion "image.Ok()" failed at ..\..\src\msw\bi
tmap.cpp(799) in wxBitmap::CreateFromImage(): invalid image

import wx
import os
import ThumbnailCtrl as TC
#-----------------------------------------------------Class ThumbnailSimple
class ThumbnailSimple(wx.Frame):

     def __init__(self):
         wx.Frame.__init__(self, None, -1, title='Thumbnail Simple')
         self.panel = wx.Panel(self, -1)
         self.TC = TC.ThumbnailCtrl(self.panel, -1)
         self.dirbutton = wx.Button(self.panel, -1, "Select Image Directory")
         # sizer -- Create, Add and Set
         sizer = wx.BoxSizer(wx.VERTICAL)
         sizer.Add(self.TC,1,wx.EXPAND,1)
         sizer.Add(self.dirbutton, 0, wx.CENTER, 1)
         self.panel.SetSizer(sizer)
         sizer.Layout()

         self.Bind(wx.EVT_BUTTON, self.OnSetDirectory, self.dirbutton)
         self.TC.Bind(TC.EVT_THUMBNAILS_POINTED, self.OnPointed)
#-----------------------------------------------------------------Handlers
     def OnSetDirectory(self, event):
         dlg = wx.DirDialog(self, "Choose a directory with images:", defaultPath=os.getcwd())
         if dlg.ShowModal() == wx.ID_OK:
             self.TC.ShowDir(dlg.GetPath())
             print("OnSetDirectory: directory changed to: %s\n"%dlg.GetPath())
         dlg.Destroy()

     def OnPointed(self, event):
         print("OnPointed: Thumb pointed: %s\n"%self.TC.GetPointed())
         event.Skip()
#-----------------------------------------------------------------MainLoop
if __name__ == '__main__':
     app = wx.PySimpleApp()
     frame = ThumbnailSimple().Show()
     app.MainLoop()