calling python function from windowproc in win32

[Gabor Papp]

I'm trying to call a python function back from a win32 windowproc.
I pass a hwnd of a Toplevel window to a C initalization function
from python. I hook my own windowproc to the existing window 
like this:

pWndProc = SetWindowLong( hwnd, GWL_WNDPROC, (long)(WNDPROC)MyWindowProc
);

my windowproc looks something like this:

LRESULT CALLBACK MyWindowProc( HWND hwnd, UINT uMsg, WPARAM wParam,
LPARAM lParam )
{
    if(uMsg == WM_COMMAND)
    {  
        PyObject_CallFunction( myCallback, NULL );
	return 0;
    }
    return CallWindowProc( pWndProc, hwnd, uMsg, wParam, lParam );
}

This callback cause a page fault in python15.dll, but it works fine if
I call this from a normal C function and not a windowproc. I suspect
some thread problems.

Thanks for your help,
Gabor Papp