Q: ERROR extracting files from the package Essentials.pkg.

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Repair the Hard Drive and Permissions - Yosemite, Mavericks, Mountain Lion or Lion

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Repair

When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list.  In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive.  If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported then click on the Repair Permissions button. When the process is completed, then quit DU and return to the main menu. Select Restart from the Apple menu.

Do you have a backup of the system you are trying to upgrade?

Then I'm afraid you will need to reinstall OS X from scratch. To do so will require that you erase the drive and install either the original OS version that came with your computer when it was new on the two DVDs that were in the box or install the retail Snow Leopard DVD you used to upgrade your computer to 10.6.3.

Clean Install of Snow Leopard

     1. Boot the computer using the Snow Leopard Installer Disc or the Disc 1 that came

         with your computer.  Insert the disc into the optical drive and restart the computer.

         After the chime press and hold down the  "C" key.  Release the key when you see

         a small spinning gear appear below the dark gray Apple logo.

     2. After the installer loads select your language and click on the Continue

         button. When the menu bar appears select Disk Utility from the Utilities menu.

         After DU loads select the hard drive entry from the left side list (mfgr.'s ID and drive

         size.)  Click on the Partition tab in the DU main window.  Set the number of

         partitions to one (1) from the Partitions drop down menu, click on Options button

         and select GUID, click on OK, then set the format type to MacOS Extended

         (Journaled, if supported), then click on the Apply button.

     3. When the formatting has completed quit DU and return to the installer.  Proceed

         with the OS X installation and follow the directions included with the installer.

     4. When the installation has completed your computer will Restart into the Setup

         Assistant. Be sure you configure your initial admin account with the exact same

         username and password that you used on your old drive. After you finish Setup

         Assistant will complete the installation after which you will be running a fresh

         install of OS X.  You can now begin the update process by opening Software

         Update and installing all recommended updates to bring your installation current.

Download and install Mac OS X 10.6.8 Update Combo v1.1.

Then please tell us what is currently installed on the external drive?

Reinstalling OS X Without Erasing the Drive

Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.

When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list.  In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive.  If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Continue button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.

Also see:

Reinstall OS X Without Erasing the Drive

OS X Yosemite- Reinstall OS X

OS X Mavericks- Reinstall OS X

OS X Mountain Lion- Reinstall OS X

OS X Lion- Reinstall Mac OS X

     Note: You will need an active Internet connection. I suggest using Ethernet

                 if possible because it is three times faster than wireless.

If the above is not doable, then do this:

Install or Reinstall OS X from Scratch

Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Erase the hard drive:

  1. Select Disk Utility from the main menu and click on the Continue button.

  2. After DU loads select your startup volume (usually Macintosh HD) from the

      left side list. Click on the Erase tab in the DU main window.

  3. Set the format type to Mac OS Extended (Journaled.) Optionally, click on

      the Security button and set the Zero Data option to one-pass. Click on

      the Erase button and wait until the process has completed.

  4. Quit DU and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Install button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible

           because it is three times faster than wireless.

This should install the original version of OS X that came on the machine. You can then upgrade to Yosemite.

I have an iMac 27 Mid2010 and ran into the same issue. Yep, its the memory. As soon as I installed the original Apple memory (thank God I still had it) it ran through without any issue.

The first time I ran into this was "upgrading" from Mavrick. After getting through it then re-installing my new Non-Apple memory, the system was very unstable. Most application would crash, Apple products, Adobe, etc.. very unstable and pretty much unusable. I then reverted back to Maverick.

After speaking to a Mac friend of mine, he suggested installing Yosemite fresh and dont upgrade.. Just wipe out and start clean. Just completed that process. Here I had to, again, install the original Apple memory to get through the install. Right now everything is very stable, but I have NOT re-installed my Non-Apple memory yet.

So my tests are not 100% complete yet, but there is the possability or problems running Yosemite with Non-Apple memory even if you get past the installation. OR ((and I hope this is the case)) the upgrade process just ***** and fresh install is the way to go.

If you no longer have your original Apple memory (I am so sorry) but there may be some hope. You need to find out who manufactured the memory for your machine at that time and get a model number. Then try and track down. If its an older system, that may be tough. But a similar experience I had years ago with my G4 Mac, makes me think there is still hope. I was looking to create video DVD's and since my model only came with a DVD-RAM at the time, I couldnt do it.. Or at least iDVD would recognize it. I decided to but a 3rd party DVD Writer and replace the DVD-RAM. Simple, right? Nope, not by a long shot.. As I researched it I found out it wasnt that simple you coulndt just buy any DVD-Writer, iDVD would completely ignore it. The solution I discovered was to find the exact model drive that was shipping with that Mac model at the time and purchase one of those. I knew Apple wasnt producing some special drive for the Mac and they had to be getting them from somewhere, so they pick one specific model to use and geared their software towards it.. I found one for a very reasonable, non inflated Apple price, installed it and was able to successfully get past iDVD's hangups and could go on my merry way. So I think the same solution will apply to Memory as well.

Hope this helps!