locating source of buffered exceptions?

Our wx application is showing a flood of exceptions on shutdown, line after line of:

Exception exceptions.TypeError: "'NoneType' object is not callable" in <wx.lib.pubsub._NodeCallback instance at 0x1799e40> ignored
Exception exceptions.TypeError: "'NoneType' object is not callable" in <wx.lib.pubsub._NodeCallback instance at 0x17a0030> ignored
Exception exceptions.TypeError: "'NoneType' object is not callable" in <wx.lib.pubsub._NodeCallback instance at 0x17a0120> ignored
Exception exceptions.TypeError: "'NoneType' object is not callable" in <wx.lib.pubsub._NodeCallback instance at 0x17ba0a8> ignored
Exception exceptions.TypeError: "'NoneType' object is not callable" in <wx.lib.pubsub._NodeCallback instance at 0x17a0e68> ignored
Exception exceptions.TypeError: "'NoneType' object is not callable" in <wx.lib.pubsub._NodeCallback instance at 0x17a73a0> ignored
Exception exceptions.TypeError: "'NoneType' object is not callable" in <wx.lib.pubsub._NodeCallback instance at 0x17a0580> ignored
Exception exceptions.TypeError: "'NoneType' object is not callable" in <wx.lib.pubsub._NodeCallback instance at 0x17a03a0> ignored
Exception exceptions.TypeError: "'NoneType' object is not callable" in <wx.lib.pubsub._NodeCallback instance at 0x17a0a80> ignored
Exception exceptions.TypeError: "'NoneType' object is not callable" in <wx.lib.pubsub._NodeCallback instance at 0x17ba440> ignored
Exception exceptions.TypeError: "'NoneType' object is not callable" in <wx.lib.pubsub._NodeCallback instance at 0x17a7da0> ignored
Exception exceptions.TypeError: "'NoneType' object is not callable" in <wx.lib.pubsub._NodeCallback instance at 0x1723378> ignored

We are having trouble isolating the source of the problem. Any advice would be much
appreciated.

Cheers,
Darran.

Darran Edmundson (darran.edmundson@anu.edu.au)
ANU Supercomputer Facility Vizlab
Australian National University, Canberra, ACT 2600
tel: +61 2 6125-0517 fax: +61 2 6125-5088