Looks as if there are two problems here. The first is that Guide
attempts to download this file :
This contains data for most comets since about 1995, and I've
found it to be an excellent resource. The problem is that it is
updated on an irregular schedule (sometimes a few months go by
between updates), so it has to be supplemented by the 'soft02cmt.txt'
file from the Minor Planet Center. 'soft02cmt.txt' is usually quite
up to date, but it drops comets when they are considered unobservable.
So Guide really needs both datasets. (Plus, as Denis mentions, a
third dataset, built into the DVD, for pre-1995 comets. It is
this dataset, 'cometg.dat', that Guide uses if you've set its
date/time back by twenty years or more.)
Anyway. I was able to access ELTDAT.TXT a few days ago. Now,
it's failing. (As is an attempt to access www.imcce.fr itself.)
The second problem is that Guide is responding to this error by
going into a loop of error messages, instead of just saying,
"Sorry, can't update that file; I'll just carry on and update
'soft02cmt.txt'." I will investigate.
(A final side note: for historical reasons, Guide downloads
'soft02cmt.txt' and renames it to 'soft02cm.txt'.)