Issue

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.

Resolution

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

Clear NVRAM

• 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)