Q: An error occurred while preparing the installation. Try running this application again.

Gah, "it just works" was not quite the case this time but I got it to work!  I have an early 2008 Mac Pro with a RAID array and OS X 10.6.6.  I downloaded Lion and got the infamously vague error message.  I then tried the following in not necessarily this order:

1) First I tried zapping the PRAM by holding down command-option-P-R all at once during startup.  Nothing happened.   Then I remembered tip #1: For some reason, at least on my Mac, the keyboard only works during startup if plugged into the front of my mac, not if it is plugged into my monitor.  This time I got two startup chimes like I'm supposed to, showing it was indeed zapped.  Anyway, still didn't help.

2) Then I tried running disk utility from my installation disk and sure enough there were some problems with the disk which it fixed.  Still didn't help Lion get installed.

3) I followed the nice instructions on how to burn your own Lion installation disk at: http://mashable.com/2011/07/20/lion-clean-install-guide/#20859Step-1-Download-Li on-From-the-Mac-App-Store

When I ran the install disk from the resulting installation disk I still got failure but this time it took the form of the installer freezing up during a "checking disk" message.  Sigh...

4) I checked the hardware requirements but a Xeon Mac Pro is indeed Lion material.

5) On the theory that maybe the RAID array was causing problems, I used the Lion installation disk to undo the RAID (after a full backup!) and then redid it using its disk utility.  Still no good.  And Mail crashes now.  Sigh.

6) Started looking up prices for new Macs and getting sticker shock.

7) Suddenly inspiration!  The "checking disks" error caused me to remember reading something once about external firewire disks causing problems.  I unplugged my WD external firewire disk drive (that I use for TimeVault backups) and tried again with my Lion installation disk.  Success! 

Anyway, hope my bedraggled saga will be helpful to someone.

Hi all,

I get this same error message. I have unplugged my external hard drive and reset the PRAM, but I still get the same error. Is there any official help on this? Is there any generally agreed upon solution?

My main drive is formatted using softRAID. Could that be a source of the problem? I have a 2008 Mac Pro. Thanks.

Hi all,

Apple may have posted a solution to this for me: Software RAID - in my case SoftRAID.

Please see the following Apple Support article:

OS X Lion: Upgrading from Mac OS X v10.6 does not work with software RAID; "An error occurred while preparing the installation. Try running this application again." appears

http://support.apple.com/kb/TS4212?viewlocale=en_US&locale=en_US

Hopefully this will work for me. Thanks.

Apple's resolution did not work for me. I get the same error running the Lion install from an external FW800 disk to a Mac mini server's internal RAID volume that is running OS X server 10.6.8. I may try the DVD method next.

Zapping the PRAM worked for me as well.

This (copy to Applications folder, and then run it) worked for me on Mac Air (original release version).  Lion simply did not like installing from external DVDROM at all.

Thank you, Mr. Marron.

Try restarting your computer holding down the 'Shift' Key.  This will do a "SAFE BOOT".  After doing that

Lion installed with no problem.  Hope this works for somebody else.  got this tip from a 'Supervisor' Tech at Apple.

This what worked for me. Many thanks

I'm posting because I had the same problem, and none of the fixes in this thread worked for me. I'm also guessing a few people might want to scrap Mavericks and come back to Lion, or Mountain Lion, so hopefully my 8 wasted hours helps someone else. I was running OS X Mavericks for about 2 weeks, which ***** on my mid 2010 MBP, 4GB RAM. Since Apple makes anything other than an upgrade excruciating (read: impossible), I just blew away the whole hard drive and started over. Easy, right? Let's just say I was 5 minutes from abandoning Apple for Linux permanently. Ok, end gripe.

So, for whatever reason, the issue seems to have been related to installing from DVD. I don't care enough to explore why that might be, since I found my workaround. I downloaded the installer, burned to DVD, booted from DVD, went through the "Preparing to Install" motions about 8 times. This is pretty vanilla stuff - empty hard drive, one partition, all erased / formatted with Apple's own install media. I initially stuck with the single partition - Macintosh HD. It would never hang mid way - always would get through 100% of the preparing to install phase, and then the same error.

In an attempt to eliminate causes, I figured it would be handy if I could somehow run the same install package from the hard drive instead of the DVD. Unfortunately, I had already deleted the OS, so I had to boot into the DVD. So, while in the DVD install, I ran the Disk Utility, created 2 partitions (one Macintosh HD, and one 15GB partition for OS X Lion Install). Once that was done, still in the Disk Utility, I clicked on the SuperDisk Volume on the left (the DVD installer), and then the "Restore" tab. This effectively allows to to clone one Volume to another. So if you set the source to be the DVD Install Disk, and the Destination to be your newly minted Hard Drive partition, next time you reboot you can eject the DVD and the installer will boot from the HD. This time, it worked like a charm! Again, no idea why it would keep failing while running from the DVD drive, and work from the HD.

Hope that helps someone.

Cheers.

I was trying to do a clean install, and had this error over and over, but then I found this video that worked just perfectly for me.

My computer was with a date of 2000.

Fixed it and it worked =D

https://www.youtube.com/watch?v=Cf4TzZt24-M

@ranato.gama - Thanks so much for posting that video! Solved my problem I forgot that my computer occasionally will set its internal clock back to 2000. Does this happen to anyone else? Is there a way to fix this?

I had major issues on my 2008 15" MBP laptop where it would freeze and run really slowly after installing Mavericks.

Tried a SMC reset, which didn't do anything noticable for me.

Tried installing Lion to rever to an OS that was older (like my laptop), but kept getting the error metioned in this thread.

Then I installed a new HD. Same problem, couldn't get past the errror mentioned in this thread.

Then finally tried a NVRAM reset which got me into the actuall isntallation process. It seems to be actually isntalling now!

I noticed an instant performance increase after the reset, even on Disk Utility. I might not have even needed a new HD.

Reset your NVRAM: http://support.apple.com/kb/ht1379

I'll post back if it doesn't end up fully installing. Maybe a NVRAM reset would have sped up Mavericks. Should I try installing Mavericks again or stick with Lion. Not sure...! Probably will play it safe for awhile.

Good luck everyone!

Wow, after 6 hours, rebooting, repairing, reloading - checking the date in the Terminal and correcting it, finally resolved my installation nightmare.  Thank you - Renato!  

Thank you! I was restoring my mid-2010 macbook pro and this solved my issue. Hadn't turned it on in a while and date was wrong. Thank you! Hope that video never gets taken down!

Omg this WORKED! Spent a long time trying everything under the sun, and here is the solution!  Thanks so much!