Hi Ian,

Because the issue affects (210) Isabella and not (1) Ceres, I suspect
that the MPCORB elements are getting overridden by ones downloaded for,
say, "Critical-List Objects" or "Unusual Objects". Take a look in
Extras... Asteroid/Comet Options, then click on Edit Comet/Asteroid
Data. Scroll down and look for (210) Isabella; click on it, then on
Delete.

Possibly a better move would be just to download this file:

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

to your Guide folder. That will provide you with an up-to-date set
of comets, _without_ any "pollution" from the Critical-List or Unusual
Objects.

Basically, use of the "Critical-List" or "Unusual Object" options is
almost never a good idea, for exactly the reason you're discovering: it
causes conflict with any other list of elements one might be using,
such as MPCORB. But downloading a corrected 'comets.dat' ought to
cause the issues to vanish.

> I am using XP as I could never overcome the display issues and crashes
> on my Windows 7 PC when zooming in further than level 7.

That doesn't sound at all good.

Are you using a current version of Guide 8? I'd suggest going to

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

and downloading the current version, and unZIPping that in your Guide
folder. It sounds as if something has gotten corrupted in Guide. Usually,
grabbing the current update makes such "mystery crashes" vanish.

If it does not, I very much would like to know about it. I can suggest
some steps for puzzling out the error, which will start with "shut as much
off as you can; zoom in to level 8; turn things back on one by one, and
see if you can narrow down what causes the crashes."

-- Bill