wxPython error "can't set focus to invalid window"

[omission9]

An application I have written is, suddenly it seems, throwing the
following error after being left in use for several hours. This does
not seem to occur with lighter usage. I am not 100% sure what causes
this? Anyone have any advice? Seen it before?

Traceback (most recent call last):
File "PythonCardPrototype\binding.pyo", line 304, in _dispatch
File "wxPython\events.pyo", line 23, in GetEventType
wxPython.wxc.wxPyAssertionError: C++ assertion "wxAssertFailure"
failed in e:\Projects\wx2.4\src\msw\window.cpp(454): can't set focus
to invalid window

 

[omission9]

An application I have written is, suddenly it seems, throwing the
following error after being left in use for several hours. This does
not seem to occur with lighter usage. I am not 100% sure what causes
this? Anyone have any advice? Seen it before?

Traceback (most recent call last):
File "PythonCardPrototype\binding.pyo", line 304, in _dispatch
File "wxPython\events.pyo", line 23, in GetEventType
wxPython.wxc.wxPyAssertionError: C++ assertion "wxAssertFailure"
failed in e:\Projects\wx2.4\src\msw\window.cpp(454): can't set focus
to invalid window

To clarify this further this seems to occur when the application has
been left running for several hours and the application has been
minimized to the Windows task bar. The error happens when the user
tries to maximize the window. The application has a child thread
running(simply polls a dircetory and processes some text files) in the
background.
Does this help jog anyone's memory of what his could be? Blame
windows?