Fix “can't be verified” and “error occurred while preparing the installation” errors on OS X

Error message when installing OS X El Capitan.

My reader Peter wrote to me a few days ago that he gets a strange error message when installing OS X El Capitan and after that he can only press “OK”, which aborts the installation. The exact wording of the error is:

This copy of the Install OS X El Capitan application can't be verified. It may have been corrupted or tampered with during downloading.

At first it sounds like you've caught a contaminated download that may contain malware, but I can give the all-clear here. This error message usually occurs when installing OS X El Capitan or OS X Yosemite because the Mac has not set the correct time or date.

"This copy of the Install OS X Yosemite application can't be verified. It may have been corrupted or tampered with during downloading." - With this the OS X El Capitan Installer quits its service.
“This copy of the Install OS X Yosemite application can't be verified. It may have been corrupted or tampered with during downloading.” – the OS X El Capitan Installer quits with this. @Peter: Thanks for the screenshot.

This error is also not uncommon:

An error occurred while preparing the installation. Try Running Again.

Sometimes these errors can also be fixed by simply restarting your Mac and starting the installation from scratch. And to rule out the unlikely (but possible) case that the OS X installer is damaged, you should also try a newly downloaded installer.

However, if it does not run properly the second time, then it could be that changing the system time and date on the Mac is the solution.

Set the system time on the Mac correctly

The easiest way to set the system time and date on Mac is to use the “Set date and time automatically” option. You can find these under

Apple menu (top left)> System Preferences> Date & Time

However, this only works if the Mac is connected to the Internet and can get the current time from a timeserver such as

At the top left, check the box to automatically obtain the date and time from an Apple time server.
At the top left, check the box to automatically obtain the date and time from an Apple time server.

Set the date and time manually

If the Mac is not connected to the Internet and you do not have access to the system settings, which you can also use to set the time manually, then the only way is via the Port. This can also be accessed from the OS X installation boot menu by opening the "Utilities" menu and selecting "Terminal".

If you now enter the command “date” at the command prompt (confirm with return), you will get the current system time of the Mac as output. If you notice a deviation from the actual time or date here, you can be almost certain that the error message can be corrected by setting the correct time.

The time that the Mac is currently using can be queried with the terminal and the "date" command.
You can use the terminal and the “date” command to query the time that the Mac is currently using.

The year is particularly important for the OS X installer. If the current system year is before the year in which the corresponding OS X version was released, this is an indication for the installer that something is wrong here.

There are two ways to supply the Mac with the current time:

Set the time server with the terminal

Again, this assumes an internet connection, but it would be the most elegant solution to the problem. To do this, enter the following command in the terminal:

ntpdate -u

Set the date and time with the terminal

If the Mac has no Internet, you can still set the date and time with the terminal. The corresponding command is:

Date Mmddhhmbyy

That looks a bit confused, but has a simple explanation because the letters must be replaced by the corresponding numbers. So in English Month Date Hour Minute Year. Everything is entered in one piece and without spaces, whereby each numerical value is always two-digit:

  • mm = month as a two-digit number (e.g. September = 09)
  • dd = date of the day (e.g. 7. = 07)
  • HH = hour (e.g. 16 p.m. = 16 p.m.)
  • MM = minute (e.g. 43rd minute = 43)
  • yy = year (e.g. 2019 = 19)

That is, for September 7, 2019 at 16:43 p.m. the command would look like this:

dates 0907164319

If you have set the time again this way (don't forget to return!), You can close the terminal and start the installation process again and it is highly likely that the Mac will no longer throw these strange error messages.

macOS and OS X installers only from trusted sources

If the error messages really continue to be thrown, it could indeed be because something was changed in the installer. For this reason, I recommend that you only load the installers for OS X and macOS from trustworthy sources. This does NOT include buying a DVD on eBay. A reader has already reported here that he received a self-burned DVD that didn't even work. Another had been sent a DVD on which the virus scanner even hit.

Likewise, I would keep my hands off dubious-looking download sites. In case of doubt, you only catch malware and viruses here and you have a system that has been completely provided with gateways for hackers.

Perhaps you have friends with a Mac who still have an old system at their disposal. For years I've kept all Apple systems on an external hard drive in case I need them again. At this point perhaps the reference to my article with the download options for old macOS / OS X systems.


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4 Responses to “Fix “can't be verified” and “error occurred while preparing the installation” on OS X”

  1. Yes Apple, I have had bad experience with outdated operating systems and Ebay DVD. An update worked after the installation, but the computer kept crashing. Hardware tests were always great and after weeks of work I'm fed up. I butchered the Mac and only kept the 27 ″ display. You can buy a set of boards for € 70 and convert the display to a normal monitor. I will be happy to report when I have the parts.
    I once paid 800 Swiss Francs for a mid-2011er. A lot of money for me. I save the monitor with the high resolution with 400, - Francs. Then comes to a PC. The original graphics card is sold at dream prices and if I put the rest of the electronics on Ebay from 1 €, faster I5, RAM, graphics card and CD drive with all fans, cables and climborium, then I might get by with one more experience and not too many thalers less the number out.
    It's just a shame that the software you bought can't be converted?
    Anyway, I'm not waiting for answers….

    1. Hi Michael! Oh, interesting about the hardware conversion kit. I did not know! I would be happy if you would report how the conversion went and how the new “monitor” would perform. Then I wish you every success with the sale, so that you don't make too much loss. LG!

  2. Hi all,
    A similar error message regarding the installation of old Mac OS versions like Yosemite, Mavericks or similar could only be fixed by setting the date back a few years!
    Apparently there is also an SSL certificate with an expiration date in the installation file.
    In any case, I always got the message that the image could not be verified.
    Only when the date was changed to the year after the release of the respective Mac OS was I able to carry out the installation with exactly the same image without errors.

    I had that on some Macs, so it wasn't a flash in the pan, but absolutely reproducible.

    Many greetings Joachim

    1. Hello Joachim! Thanks for your report. That's interesting ... but would be perfectly understandable with the SSL certificate. Good tip!

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