There are no versions of Mac OS X available on your old Mac

Question

Task: Migrate from iMac G5, OS X 10.4.11 to Intel iMac, OS X 10.5 using Setup Assistant.
I bought the Intel Mac from my son in perfect working order in a very vanilla kind of configuration. Rather than using the Migration Assistant and re-installing my old PPC applications, particularly, Microsoft Office 2004, I decided to reinstall the OS from scratch, so I could migrate everything using Setup Assistant.
When prompted by the Setup Assistant, I connected the two systems with a Firewire 400 cable, rebooted the G5 in Target Disk Mode and waited for the magic to begin. Instead, I got the error message:
"There are no versions of Mac OS X available on your old Mac"
My old iMac was not physically connected to any other Firewire device and only to the keyboard via USB.
I used “Continue” several times at this point to try again; the result was nil response after up to 15 minutes. I used “Go Back” several times here also to, reseat the firewire cable connectors, substitute a new firewire 400 cable, try an Ethernet cable, and reboot my old iMac in target mode both by a cold start with the “T” key depressed and by restarting by using “System Preferences/Startup Disk/Restart/Target Disk Mode.” After trying to read the disk on my old IMac G5, my Intel iMac gave me this same error message every time.
When I reboot my old iMac, the OS is obviously there, so I cannot think of what is preventing the connection. I’ve been out on the web and found nothing that comes up in response to the error message, except one post at http://forums.macrumors.com/showthread.php?t=691645 for a user trying to use the Migration Assistant. His solution of mounting the old iMac as an external drive isn’t available in Setup Assistant, whose troubleshooting options at this point of the install are zip. I found nothing helpful chasing some hints at "possible firmware issues."
Man! What an unexpected, unpleasant surprise. Suggestions are welcome.
Roy

Answer 1

Of significance did your G5's drive mount on your new computer's Desktop when you connected them and booted the G5 into TDM? If it does then skip using Setup Assistant. I would first give Migration Assistant (on the new computer) a try. Or you can use common backup software to "backup" what you want from the old computer to the new one over the Firewire link.
If you don't have other backup software to use then you can use Carbon Copy Cloner - CNet Downloads or MacUpdate - which is freely available. SuperDuper! is also a good choice if you already have a purchased copy. See the following for other options:
Backup Software Recommendations
Backuplist
Carbon Copy Cloner
Data Backup
Deja Vu
iBackup
JaBack
Silver Keeper
MimMac
Retrospect
Super Flexible File Synchronizer
SuperDuper!
Synchronize Pro! X
SyncTwoFolders
Synk Pro
Synk Standard
Tri-Backup
Others may be found at VersionTracker or MacUpdate.
Visit The XLab FAQs and read the FAQ on backup and restore. Also read How to Back Up and Restore Your Files.