My Maverick download failed several times, as the file is c5gb and I have a slow broadband connection I didn't want to sit watching the progress bar for several hours and so I didn't see anything or spot when it stopped.
I had turned off any energy saving settings and my timemachine in case they were interrupting the download process. My firewall is ON.
I had previouslly used disk utility (as recommended) to repair any permission errors (which there were loads).
On one of the occasions it failed, I was there when a message popped up something like "do you want to quit all applications". Thus I firgured something was trying to close things down.
I read somewhere else about preventing SLEEP kicking in using a terminal command called <pmset>.
So I went into the terminal app and at the prompt typed
<pmset noidle>
Then restarted the download from the app store. The download process then worked in one go, albeit taking about 4-5 hrs. Then another one hour or so for the actual installation.
Hope this tip helps others ...