Have re-downloaded Mountain Lion at least 4 or 5 times, I have erased, repartitioned, and replaced hard drives and it seems no matter what I do, including removing one 4 GB sim from the laptop. ( Macbook Pro mid 2009 ). It fails. I have created and recreated a boot drive on a 8 GB USB and a 32 GB SDHC card. I when I had Lion on the laptop I had also made sure the apple ID account is the same for the computer in User/Groups as it was for the download of Mountain Lion. I have used Apple Macintosh since my first Mac SE in 1997. With all the posts on this issue on the web and the last 4 days I have spent working countless hours on this. It seems that Apple is going to be loosing clientel and market share. I would like to simply install an upgrade to the operating system. If there is anyone that can help with something I have not done that will allow me to install Mountain Lion on this Mac I would very much appreciate it.
Result on SL install attempt 3:
Mac OS X could not be installed on your computer
The Installer could not copy the necessary support files.
Click Restart to restart your computer and try installing again."
This MBP has 2 - 4GB memory simms that were installed a few months ago. I seem to recall when I first bought this MBP the max memory upgrade was 4 GB with 2 ea. 2 GB sims, which I did install in 2010. Then this year saw that 2 ea. 4 GB simms could be installed. I don't know if it is related, but SL being an older system perhaps it causes an error? I will try again with the original simms before I attempt the not recommened installation from the iMac to the MBP start up drive.