Installing Mac OS - An error occurred while preparing the installation...


Installing Mac OS X on iMac's blank formatted hard drive. Installation runs for 5-10 minutes and then fails with following error:

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

Tried installing OS X El Capitan (10.11) and OS X Sierra (10.12) - the same error occurs in both cases.


Issue was resolved by fixing incorrect time on the iMac and then clearing NVRAM.

Fix incorrect time

  •  Boot from Mac OS X installation disk / USB.
  • Go to Utilities > Terminal.
  • Type date to check the current date and time.
  • If it's incorrect, run following to fix the date and time: date mmddHHMMyyyy
    Where: mm - month, dd - day, HH - hour, MM - minute, yyyy - year


  • Shut down the Mac
  • Start the Mac and as soon as you hear startup chime press and hold keys Command + Option + P + R.
  • Keep holding the keys until Mac reboots and you hear another startup chime.


iMac 21.5'' (2009)
Mac OS X El Capitan (10.11)
Mac OS X Sierra (10.12)


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