Hi,

I get the same problem. I am using Guide 9.1 (as in "About Guide", although the title bar still says Guide 9.0) from 10 Dec 2015.

One workaround is to download comet elements for Guide from:
http://www.minorplanetcenter.org/iau/Ephemerides/Comets/SoftwareComets.html

and then manually install them from the downloaded file.

John