Upgrading from Leopard to Lion

First thing to check when these sorts of issues occur is the installer log, if you can get to it. If the installer doesn't even get that far, then check the status of your disk with Disk Utility (click Verify Disk). If it reports problems, have Disk Utility attempt to repair them.

 

First thing, make sure you backup ALL your user created data worth saving and have your existing app installers handy.

Dumb question but the picture of the big cat on the dvd itself is the white Leopard, right? Just want to make sure you aren't attempting to use a burned dvd with a possibly incorrect version of the OS on it.

Usually that error is caused by someone using the grey OEM dvd that comes with a new computer rather than the retail DVD which has the picture of the big cat on it.

If you are using a burned dvd, then its possible that the version you have is the non-retail and just literally can't be used on your computer.

Now if everything I said above is a non-issue/dumb/whatever, restart the mac to the retail SL dvd and when you get to the installer, click on Utilities at the top and choose Disk Utility and then highlight your drive, and then click on the Partition tab and recreate a new partition and then you should be able to install SL. It just might be something funky with your current hard drive format for whatever reason. What you would be doing is deleting your existing drive and recreating it from scratch.

When you are done, just restore your backed up user created data and reinstall your apps and you should be good to go.

 

From what I've seen those two statements are incompatible. That message is what you get when using a disc that is not a retail version. ("Retail copy" is an oxymoron. In theory, every one that Apple produced was an original, even though they pressed thousands of them.)

 

For future reference, the "retail" dvd is ONLY the one that you could buy at the Apple store or other software retailer. It is not the ones that come with new macs, as stated above, those are tied to specific families of machines. Macbook pro grey dvd could only be used to install the OS on certain Macbook Pros.

 

Your problem is version of the retail CD Snow Leopard is not suit for your iMac. So you should go this way:
I see that you've 1 Macbook Pro and 1 iMac. And make sure that you also have Lion Installer because the title of this thread. Pick up an USB then create a bootable USB with the Lion Installer by your Macbook Pro. Then boot from the USB to do a clean install Lion on your iMac. It must work as well. If somethings' wrong. Post your next question here and I will help you.