I wrote:
Is it safe to assume that you don't have any desktop mods or virtual desktops or anything of that sort?
Michael,
Also, you're only loading the callback patch once, right? I don't know what happens if you execute that code multiple times; it might be harmless or it might not. Graphic-Forms automatically loads it via the ASD file.
Another thing to try is to restart SBCL without the callback patch, and remove the :stdcall attribute from Alastair's code. Win32 has a special hack that allows non stdcall callbacks to be used as window procedures. This would help rule out whether that patch is causing the problem.