[MacTUG] Previously Downloaded OS X Installers No Longer Work

[Marlon A. Griffith]

"""
"A certificate is required for every app in the Mac App Store and it
turns out that all of the various OS X installers had a certificate that
expired in February 2016. Pretty much every app affected by this has
already been updated already so if you download something now, it won’t
have any issues. However, if you’re like me and like to keep a bootable
install disk or USB drive around for troubleshooting, you’ll need to
download the installer again and remake your USB drive." lifehacker

Happily, this is an easy problem to fix ahead of time:

     Delete any old OS X installers in the Applications folder or in
other locations (be sure to look on external hard drives too; if the App
Store detects an old installer, it won’t let you get a new one). These
installers have names like Install OS X El Capitan and Install OS X
Yosemite.

     Open the App Store app by choosing Apple menu > App Store.

     Click the Purchased tab. Enter your App Store password if prompted.

     Scroll down to the OS X installer you want and click Download.

http://tidbits.com/article/16302
"""