I had the same problem: download the 2.5 G, then install fails, deleting the huge downloaded file.
Here is the problem AND the solution.
The problem : the installer cannot run because of many possible reasons. For me (and it's probably the case for a lot of us), it was because there wasn't enough space left. As a rule of thumb, you need at least twice the size of the downloaded file, here 5 Gigs approximately. Don't worry, this will be freed up later.
Though the installer cannot run properly, it still performs the cleanup, that is: deleting the downloaded packages. You have to prevent it from doing this, so you don't have to start from scratch every time it fails.
The solution :
- You should start by freeing up a few Gigs of space on your main disk. If you don't have 4-5 Gigs free, get an external drive or USB stick, you'll need it later.
- Start the download.
- When the download is over and Logic asks you to type your password to install the packages, STOP THERE, DON'T TYPE YOU PASSWORD.
- Go to this location : /var/folders/k5/ (how? Go to the Finder, type command-shift-G, which is the shortcut for the GO TO FOLDER, in the GO menu.
- in /var/folders/k5/ you'll probably find sub-folders names C or T, or whatever. In one of these folders you'll find the big package you just downloaded.
- copy that package somewhere else (the USB stick or external drive might be useful if you're out of disk space)
- now go back to Logic and type your password.
- if you have enough space everything should be ok.
- if NOT : you still have the fruit of your long awaited download on the USB stick or drive. Run the package from there...
If this doesn't succeed :
- restart the Mac
- repair permissions with Disk Utility (lacking permissions might also be the reason the install failed)
- run the package again.
Again if this fails, run Utilities/Console and have a look at install.log it will tell you why. You can always copy the info here to ask for help.
I failed three times at downloading (6 hours !) before calling Apple Support and getting the bases of that solution. Now I've installed all packages.
And, by the way, if you already had the packs before buying/updating Logic, it will still tell you they need to be installed. Do it, it won't take more space on your disks. All the new packages are dated 6 december 2011 or around.
Hope this helps.