I recently purchased a used G5 Power Mac (2 x 1.8 GHz with 2 GB RAM) with System 10.4.11 installed on the 160 GB HD. It was bought to replace a Quicksilver which had been upgraded to run OS X 10.5.4 so I naturally wanted to upgrade this machine to 10.5.4.
Upon running the Install DVD using the Archive & Install option, I got an error message stating that "The BaseSystem package was not compatible with this machine and to contact the software supplier." At this stage I did not suspect a RAM problem so proceeded to install 10.5.1 on the same HD using another G5 of the same specs. It loaded OK so I moved the disk back to the "new" G5 and tried to run the Migration Assistant to recover the data files we needed.
The Migration Assistant stalled and, in the process, probably corrupted the bookkeeping file that I most wanted to access. I then suspected that the Leopard Install disk might have been faulty, since that was an implication of the error message. I bought a new Leopard Install DVD and got the same error message. I then tried to install OS X 10.4 from the install DVD but it too produced the same error message.
Finally, I started to suspect a hardware fault, so I found my copy of TechTool DeLuxe on an AppleCare CD. I ran it and discovered that the RAM test failed. I removed all 8 256 MB chips and replaced them with two good 512 MB chips from another G5. TechTool then passed all the hardware and I could proceed with the installation of OS X 10.5.1 and the upgrade to OS X 10.5.4. Three pairs of the 256MB RAM chips have passed the Tech Tool so have used these and will return the remaining pair to the vendor.
Migration Assistant was used to transfer applications, and these appear to have transferred correctly. I have pulled a good copy of the Bookkeeping file from the Time Machine backups that were running on the original G4.
It is now obvious that the vendor of this G5 had not installed OS X 10.4.11 from a DVD but had probably made a clone of the HD before installing it in this machine. It is also clear that they had not tested the RAM before listing this Mac on their web site.
My experience is thus a salutary warning to all purchasers of a used Mac. I just wish the error message that I first received had been a bit more wide ranging and less directed at a possible software issue.
[kirkmc adds: This is less of a hint than a cautionary tale, and a clue for troubleshooting certain types of problems. I've had problems with bad RAM a few times over the years, and especially recall the early days of Mac OS X, which was much more sensitive to RAM than OS 9. I had an iMac DV SE, and installed OS X 10.1 on it. It ran fine for a while, but then would crash or kernel panic. It turned out that I had two RAM cards in it, the second of which was bad; when the Mac needed to access more than the first card's memory, it had problems. Replacing the second card resolved my problems.]
Mac OS X Hints