Hi Lawrence, all,

Still not clear on why this is happening, but there are a
couple of things I'd suggest trying.

One is to download this file:

http://www.projectpluto.com/comets.dat

This is a current, up-to-date list of comets, gathered mostly
from Patrick Rocher's list of comet orbital elements:

http://www.imcce.fr/fr/ephemerides/donnees/comets/ASCII/ELTDAT.TXT

I suggest using this for several reasons. First off, it will
bring you up-to-date without having to worry about the apparently
flaky nature of MPC downloads. Second, I think better of Rocher's
list than the MPC one. He's including _all_ objects, not just
the 'currently visible' ones, and provides more data for each
object. In the future, this may enable Guide to simply download
a new comet orbital element database, instead of having to do some
incredibly strange things to merge the MPC's "current" list with
its list of historical comets. Eventually, I expect to set up
Guide to be able to use either list.

Secondly, the list you have will be "clean". Because of the
bizarre nomenclature scheme for comets, you can download an object
with a name such as "P/Hill (P/2008 X1)" from MPC, and then some
time later get the exact same object as "P/Hill (211P)". Guide
has no way of knowing that the objects are one and the same. The
'comets.dat' on my Web site has such spurious doubles fixed.

Third... I'm wondering if some of the issues people are encountering
involve corrupted 'comets.dat'. If so, replacing with an uncorrupted
version might be in order anyway.

OK, so given the above, you should be all set for the nonce.
If you then try Guide's update function in a week or so and it doesn't
work, I'd recommend (as others have suggested) attempting to download
this file:

www.minorplanetcenter.org/iau/Ephemerides/Comets/Soft02Cmt.txt

If you can't get that file, then you can assume Guide can't get it
either. (Please let me know if this happens. In theory, at least, if
Guide can't get the file, it should give an error message to that effect,
suggesting that you try later. It shouldn't crash or hang or give weird
messages.)

Anyway. Having downloaded the file, try going to Extras... Asteroid/Comet
Options, then "Add MPC Comets", and then click on the line at the bottom of
the resulting window: "Add MPC asteroids/comets". Select the Soft02Cmt.txt
file that you've just downloaded.

By doing this, you've done almost exactly what is supposed to happen
when clicking on "Click to download updated comet data and add it to Guide".
However, you've broken apart the "download" part from the "update" part,
so we can see which half isn't working.

-- Bill