El Capitan installation failed (error related to essentials.pkg)
I have a late 2012 27" iMac which was running Yosemite.
Today, when I tried to upgrade to El Capitan I repeatedly get the message:
OS X could not be installed on your computer
An error occurred while extracting files from the package "Essentials.pkg".
Quit the installer to restart your computer and try again.
I have tried repeatedly and keep getting the same error. Googling indicated that it may be a problem with non-Apple-memory -- I had 32 GB Crucial RAM -- so I replaced it with the RAM modules that originally came with the iMac but I ended up with the same error message.
How can I see details about what this error is? Should I go back to Yosemite (I do have up-to-date Time Machine Backups)? Any suggested fixes?
iMac (27-inch, Late 2012), OS X Yosemite (10.10.3)