To fix the aforementioned “unspecified error”, follow the steps below:

    First, click “OK” on the error window.
    Then click on “Utilities”, then “Terminal”.
    Once opened type in “date” without the quotes and hit enter. This will give you the computer’s current time and date.
    To fix the date, type in the current date/time in the following format: “date mmddHHMMyyyy”. (mm = two-digit month, dd = two-digit day, HH = 24 hour, MM = minute, yyyy = 4 digit year) So if it is currently 10:46am, June 19, 2015, the command would look like: “date 061910462015”.
    Once you have the current date/time inserted, you will then hit enter. You can double-check to see if it was set properly by using the “date” command once more, it should show the date/time you have just typed in (see image below).
    Once the proper date and time are set on the computer. Exit the Terminal and run the OS X installer once more. This time it should go through without any errors! If it doesn’t, feel fr