If you are having this problem in Elyssa then genisoimage could be the problem.
The version shipped with Gutsy was OK so you need to downgrade and install the slightly earlier package genisoimage (9:1.1.6-1ubuntu3)
This can be achieved as follows
Download the release for Gutsy http://packages.ubuntu.com/gutsy/genisoimage
Open a terminal in the download directory and
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sudo dpkg --force-downgrade -i genisoimage_1.1.6-1ubuntu3_i386.deb
Thanks to bedege on the Ubuntu forums for this info, thought I would pass it on.