Changing system date from Terminal – OS X recovery
When you’re booting your Mac from the recovery partition and are planning to reinstall OS X, you might be met by the following message:
An error occurred while preparing the installation. Try running again
Now, if you haven’t used your Mac for a while, the error might be caused by an incorrect system date setting. You can check this by going to utilities and opening the terminal. Once in the terminal enter the following command and hit return/enter:
The result of this command will be the date that the system currently has been set to. For some reason, it might have been reset to 2001, in which case we need to set it to the right date. To do this, we enter a new command. This command will be entered as follows:
Every bracket should be replaced with a two-digit number. For example, March 18th 2013 12:50 would become the following command:
Enter the command and hit return. You can then check if it was set correctly by running the first command again. If the date was wrong, it was likely that which caused the error, and after you quit the terminal it should be able to install OS X just fine.