mountain lion is not compatible

Hi Babowa, indeed. A "backup" of the OS after download and before install, with Lion Diskmaker (for Lion and Mountain Lion).

I've not used the Lion Diskmaker - I just use CarbonCopyCloner and make a clone (actually I have two clones of every OS version I have spread over three external hard drives).

I use CCC already twice every week, onto two different disks. but LionDiskMaker to make a bootable stick, you never know...

True.......

It's very easy to make your own backup USB sticks of ML installer, Lion Diskmaker is not needed to make a bootable backup install of the downloaded installx.dmg file, actually has not been very successful for me so I make my own. real easy

As far as the Macmini is concerned, there is no dmg file to make a bootable USB stick, which is my whole gripe! Unless I can use the downloaded file from the Internet recovery, actually had not considered this. will investigate

My Internet bandwidth is limited to 70Mb/s so 4GB is not really an issue, insignificant almost, usually download complete by the time I've made a cup of coffee. old dial up days are long gone

CCC works great for backups but my pristine original install is no longer pristine unfortunately besides a clean install is always better.

Unless I can use the downloaded file from the Internet recovery, actually had not considered this. will investigate

You need to download and once that is finished, dismiss the installer. If it is the full installer, find it in Applications folder. Copy it to a safe place somewhere else and then initiate the install process. If it's only an update, you should be able to find it in /Library/Updates (that will self destruct as well after the install is done).

I prefer my bootable clones over a USB stick (although I have one for each OS I have) A 4 GB download takes a minimum of 90 minutes here, quite often up to 3 hours - and this is not dialup. It was actually slower when I had Comcast cable (never more than 1.2 mbps at most, most of the time half that). We only have two choices here: Comcast which doesn't deliver because of 30+ year old cables and DSL which does deliver what they promise, but is somewhat slow. Not every part of the US has FIOS, not even in suburbia.

I'll give that a shot thanks

Ok, the error message is still perplexing, Apple could help the situation by making it a more meaningfull message.

In the meantime I found "Recovery Disk Assistant" http://support.apple.com/kb/HT4848 using it and the original (recovered from the trash bin) Hard Disk Drive I created a USB Install/Recovery drive.

Original Recovery HD and a USB thumb drive is required.

I believe this is all i need to install Mountain Lion from the original factory OSX 10.8.1 installation to any drive on this Mac mini6,2