callback from C DLL returning an int

My ctypes attempt is crashing the wxPython app.

This is how SetCallback is defined in the DLL:

extern "C" void __declspec(dllexport) SetCallback( long lAddress )
   {
     s_frontend.set_callback((FUNCPTR)lAddress );
   }
//The function takes in a 32-bit long pointer to a function.
//The function when defined in a calling C program should take in one 
parameter such as:

void ASLocalCode::call_back( int iMessage )

//This is fired when a new block of data is available. iMessage 
integer value is always 6.


In Python I did this:
______________________________________
...
class myADC:
   def __init__:
     ...
     self.driver = cdll.dataDll
     ...
     def data_ready_func(r):
         print r

     CB_TYPE = CFUNCTYPE(None, c_int)
     self.data_ready_ref = CB_TYPE(data_ready_func)
     print CB_TYPE, self.data_ready_ref
     self.driver.SetCallback(self.data_ready_ref)

This prints:
data_ready_func 6
then XP pops up a notice "python.exe has encountered a problem"  (the 
app is still running!), then it all closes with the XP dialog "don't 
send" button.
What is wrong here?

Ray

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