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

I have the exact same issue, later tonight i will try and boot from a dvd i.e I will burn the Lion install application to a dvd snd boot from this.  hopefully this may get around this issue.  I'll let you know.  if this dosen't work then i may have to spend a few hours on teh phone to the support help line !!

all my other updates with OSX have been smooth sailing ! not this time.

Same issue here. 2010 MacBook Pro.

Where any of you able to resolve this?

F

Lion Installer must be copied to the /Applications folder and started from there.

Download it again and try may corrupt during download just holding option click purchase then click install and besure you run the newest download so may you can trash the curren tone

Has anybody figured out a solution to upgrade? while the clean install route may work, i'm sure its not favorable for the people in this thread.

Sorry for the doulbe post, but I'd like to add I've redownloaded it twice, one of which times, the app store was my only open application and the system was under minimum load.

I'm having the exact same issue. I've tried everything and all I have is Lion sitting on my desktop. Could Apple give us an explanation for this problem?

Well this is the story so far.  Lion installed on my Macbook Pro, no issues.  However on my Imac I'm still getting the error "An error occured while preparing the instalation..." I've booted the Lion from a DVD, reintsalled snow leopard still no luck.  The next option is a phaone call to the help desk !! which I was tring to avoid.

I was able to correct this problem by resetting the PRAM and NVRAM. Took my 3 days of troubleshooting to figure it out. Also corrected some slowdown issues I was having.

Glad to hear you were able to get it installed, this fix did not work for me however.

That fix also didnt work for me. =[.  Really at the end of my rope here lol.

Since this thread seems to be gaining more speed than the other one i'm working on, i figured i'd add these images to help you all out detailing the exact problem.

--------------------------

I'm having the same issue and I wanted to provide some info specific to my mac, and some info in general to help with diganosis.

First, my specs

Secondly, I am running an aftermarket 500 GB drive.

Third, not sure if this is realated, but this screen suggests the proress will take 3 minutes, then it abruptly umps to the restart phase after about 1.5 - 2.5 minutes.

And finally, here is the seeminly unavoidable error message.

Also, other things I've tried now are
installing it from the "show package contents area",

mounting said DMG and trying to install from there.

installing a package file called "upgradeos.pkg"

no luck.