Hello all,

OK, I've got it figured out... I should have puzzled it out right away;
in hindsight, the problem is quite obvious to me.

Short version: don't use the links to download critical, unusual, or
distant objects. Update 'mpcorb.dat' instead. (I'll remove those three
links in the next update.)

Long version follows:

Once upon a time, all of the "add-on" element lists were small, with at
most a few hundred objects. But the "distant" list now contains 1717 objects;
the "unusuals" list contains 9701 objects; and the "critical list" contains
1691 objects.

This raises a dilemma. I _could_ just revise Guide to handle this sort
of thing. But it would be wrong to just bump up the limit. It puts
thousands of objects into the "added comets/asteroids" file; if you go
to Extras... Asteroid/Comet Options... Edit Comet/Asteroid Data, you
get an immense list of objects. And Guide's efforts to merge in these
MPC update files with existing asteroid data have never been completely
successful.

To quote from the dialog wherein one can download asteroid data:

"...Use of the following links [to update distant, critical-list,
and unusual objects] is not really recommended. The objects in question
already have well-determined orbits, and the latest MPC data will
represent only a small improvement. By far the best way to update
asteroids is to use MPCORB. This allows you to update Guide's asteroid
data completely. The only downside is that MPCORB is about 30 MBytes
in compressed form, a bit large for those with dial-up modems."

That last issue is getting to be less of a problem; for most of us,
a 30 MByte download is peanuts. The next update will remove the ability
to use those three links; we'll go from "updating" asteroids to just
replacing the entire asteroid dataset with a new MPCORB.DAT.

(Ideally, I'd do the same thing with comets. Sadly, there is no
way to get a complete comet database; MPC just supplies "currently
observable comets", which have to be merged with older comets in order
to have a complete list of comets.)

-- Bill