wxPyDeadObjectError

Traceback (most recent call last):
  File "c:\Eigene Dateien\python\wxpyatol\FilePanel.py", line 90, in OnSetFocus
    self.Activate(true)
  File "c:\Eigene Dateien\python\wxpyatol\FilePanel.py", line 43, in Activate
    self.m_pFileList.SetFocus()
  File "C:\PYTHON23\Lib\site-packages\wxPython\wx.py", line 1834, in __getattr__
    raise wxPyDeadObjectError( self.attrStr % self._name )

What is the reason or how can i avoid this?

Thank you in advance!

Francesco