Andrew, thanks for your response. With the help of a local self-help group I have managed to apply one of the fixes above, and thanks to those who posted them.
I remain confused at the approach. If qcad 2.2 is looking for something it needs and can't find it, because it's looking in the wrong place, then why no effort to fix qcad, but instead, making a change to a file in the operating system? I don't mean that as a rhetorical question. I would really appreciate knowing the reason.
Anyway, for those with a computer skill level closer to mine than the contributors above, here is what I did:
Go to Applications> Accessories>Terminal
Type sudo gedit /etc/cups/cupsd.conf press Enter
Type in your root password press Enter
You have indicated that you want to edit a particular file, and ubuntu has opened an editor called “gedit”,and brought into it the file you asked for.
Put the cursor at the end of any line above a # line. press Enter
This creates an empty line. A line starting with # is ignored by the system, but allows you to identify the change you are about to make to help any future trouble-shooting. So type, for example,
# yourname date fix qcad press Enter
Printcap /etc/printcap do NOT press Enter. At the top of the screen press Save.
Close this screen. Close the Terminal screen. Reboot the machine. You're done.
To Andrew or those above who know what they're doing: If there is anything wrong or particularly clumsy about the sequence I've described, please let me know. Thanks, mzee.