Hi Peter,

Nicely spotted; I was able to replicate that error readily,
and tracked it down and fixed it, and have updated

http://www.projectpluto.com/find_orb.htm

accordingly. That led to what I think is either a nice new
feature, or a bug fix, described at the above page as follows:

------ snip begins -------

(2010 Mar 12) In the course of fixing the above bug, I realized
again that making Monte Carlo variants was slow. Find_Orb computes one
such variant every half-second. For short arcs, or with no perturbers,
it could be computing far more than that. I revised the code so it would
compute Monte Carlo orbits for a quarter second, once every half second.
In short, with MC turned on, half the CPU time will be devoted to
computing Monte Carlo orbits.

I may make this user-tunable ("I want this to run in the background,
not using much CPU time, while doing other things... set it to ten percent",
versus "I'm going out for a few hours; the computer might as well crunch
Monte Carlo orbits 100% of the time.") But I've not done that yet.

------- snip ends ------

If you think I ought to have had Find_Orb work this way all along, then
this is a bug fix. If you think Find_Orb handled Monte Carlo orbits
acceptably all along (though maybe not as briskly as one would wish), then
this is a new feature. I am undecided as to which side I would take.

-- Bill