Mac os 10.11.5 installation error - "verification failed"

Hi all.

I have seen various answers to similar questions for previous versions of Mac Os X 10.11, but apparently nothing that is relevant to my problem or that has been useful so far.

I have a Macbook Pro, late 2012. Multiple attempts to update to the latest Mac Os (10.11.5) from the App Store have failed with "verification failed" when starting the actual installation after download. I'm quoting below a part of the install.log file that seems to be relevant but from which I cannot understand what is going on. Please note that the very same installation procedure worked on my newest Macbook Pro, mid 2015; the failing machine is the previous one I used, which I'm now using from home. (Perhaps, a detail that may be relevant, from what I read from previous users with similar problems, is that I upgraded my McP 2015 from my office's network while I'm using my home ADSL for the failing McP 2012).

Help would be greatly appreciated.

Extracted from /var/log/install.log:

May 21 08:17:20 oldPaoloPro system_installd[651]: installd: Starting

May 21 08:17:20 oldPaoloPro system_installd[651]: installd: uid=0, euid=0

May 21 08:17:20 oldPaoloPro system_installd[651]: PackageKit: Adding client PKInstallDaemonClient pid=248, uid=200 (/System/Library/CoreServices/Software Update.app/Contents/Resources/softwareupdated)

May 21 08:17:21 oldPaoloPro softwareupdated[248]: PackageKit: Enqueuing install with client-specified quality of service (utility)

May 21 08:17:21 oldPaoloPro system_installd[651]: PackageKit: ----- Begin install -----

May 21 08:17:21 oldPaoloPro system_installd[651]: PackageKit: request=PKInstallRequest <2 packages, destination=/>

May 21 08:17:21 oldPaoloPro system_installd[651]: PackageKit: packages=(

"PKLeopardPackage <file:///Library/Updates/031-49587/OSXUpd10.11.5.pkg>",

"PKLeopardPackage <file:///Library/Updates/031-49587/FirmwareUpdate.pkg>"

)

May 21 08:17:24 oldPaoloPro system_installd[651]: PackageKit: Will do receipt-based obsoleting for package identifier com.apple.update.firmwareupdate (prefix path=/)

May 21 08:17:24 oldPaoloPro system_installd[651]: PackageKit: Install Failed: Error Domain=PKInstallErrorDomain Code=110 "An error occurred while extracting files from the package “OSXUpd10.11.5.pkg”." UserInfo={NSUnderlyingError=0x7f84154f3dc0 {Error Domain=PKXARArchiveErrorDomain Code=101 "archive verify failed" UserInfo={NSURL=file:///Library/Updates/031-49587/OSXUpd10.11.5.pkg#Scripts, NSFileOwnerAccountID=0, NSFileHFSTypeCode=0, NSFileSystemFileNumber=7719344, NSFileExtensionHidden=false, NSFileSystemNumber=16777220, NSFileSize=628141500, NSFileGroupOwnerAccountID=0, NSFileOwnerAccountName=root, NSFilePosixPermissions=420, NSFileHFSCreatorCode=0, NSFileCreationDate=2016-05-21 05:27:19 +0000, NSFileType=NSFileTypeRegular, NSFileGroupOwnerAccountName=wheel, NSFileReferenceCount=1, NSFileModificationDate=2016-05-21 06:16:13 +0000, NSLocalizedDescription=archive verify failed}}, NSURL=file:///Library/Updates/031-49587/OSXUpd10.11.5.pkg, PKInstallPackageIdentifier=com.apple.pkg.update.os.10.11.5.15F34, NSLocalizedDescription=An error occurred while extracting files from the package “OSXUpd10.11.5.pkg”.} {

NSLocalizedDescription = "An error occurred while extracting files from the package \U201cOSXUpd10.11.5.pkg\U201d.";

NSURL = "file:///Library/Updates/031-49587/OSXUpd10.11.5.pkg";

NSUnderlyingError = "Error Domain=PKXARArchiveErrorDomain Code=101 \"archive verify failed\" UserInfo={NSURL=file:///Library/Updates/031-49587/OSXUpd10.11.5.pkg#Scripts, NSFileOwnerAccountID=0, NSFileHFSTypeCode=0, NSFileSystemFileNumber=7719344, NSFileExtensionHidden=false, NSFileSystemNumber=16777220, NSFileSize=628141500, NSFileGroupOwnerAccountID=0, NSFileOwnerAccountName=root, NSFilePosixPermissions=420, NSFileHFSCreatorCode=0, NSFileCreationDate=2016-05-21 05:27:19 +0000, NSFileType=NSFileTypeRegular, NSFileGroupOwnerAccountName=wheel, NSFileReferenceCount=1, NSFileModificationDate=2016-05-21 06:16:13 +0000, NSLocalizedDescription=archive verify failed}";

PKInstallPackageIdentifier = "com.apple.pkg.update.os.10.11.5.15F34";

}

May 21 08:17:24 oldPaoloPro system_installd[651]: PackageKit: Running idle tasks

May 21 08:17:24 oldPaoloPro system_installd[651]: PackageKit: Removing client PKInstallDaemonClient pid=248, uid=200 (/System/Library/CoreServices/Software Update.app/Contents/Resources/softwareupdated)

May 21 08:17:24 oldPaoloPro system_installd[651]: PackageKit: Done with sandbox removals

May 21 08:17:24 oldPaoloPro softwareupdated[248]: SoftwareUpdate: extraction error on install of 031-49587 (reset to download error state to allow retry): Error Domain=SUErrorDomain Code=311 "“OS X El Capitan Update” could not be verified." UserInfo={SUErrorUpdateTitle=OS X El Capitan Update, SUErrorUpdateProductKey=031-49587, NSLocalizedDescription=“OS X El Capitan Update” could not be verified.}