I recently encountered the following screen error at a client site that revealed that something was preventing a Tiger-formatted iMac from accessing network resources and logging onto the Internet:
I received the same screen message when I restarted the iMac using my bootable hard drive that I connected via firewire. Noting that the iMac was set up to access the network via Ethernet, I attached my laptop to an open RJ45 port on the Linksys router that was distributing IP addresses using DHCP. Doing so, I was able to generate a private IP address to my laptop. Taking that finding one step further, I decided to install the OS X 10.4.11 patch onto my client’s machine. That installation got rid of the IP address error and enabled the iMac to be seen by other systems over the network.