I think that Simon is exposing a bug in OS X 10.5.x (I've seen this with 10.5.5 and 10.5.6).

I have Simon running and only doing two things: mounting and immediately unmounting AFP volumes from two different local AFP servers, every 30 seconds. These are just to confirm that AFP is running and successfully able to serve a volume on these servers. Just monitoring port 548 turned out to be not sufficient, because in certain failure scenarios port 548 is up and running, but volumes won't mount.

What I found was that my FileMaker Pro 9.0v3 app was randomly crashing after I started running Simon on my machine doing these AFP checks. At first I suspected a bad database or something, but I completely reinstalled it and did the usual troubleshooting steps, but to no avail....until I paused my Simon tasks. Then all was well. I can now reproduce the crash on demand (after a random delay of a few hours or so) whenever Simon is doing those AFP mounts.

I've attached a crashlog for FileMaker FWIW. I've also noticed that my VersionTracker Pro app is also sensitive to this same issue.

I'm not sure that there's anything that Simon can do about it, but perhaps get more information to report to Apple as a bug in OS X 10.5.x?