It’s like this message has become a feature of OS X.

You download a .dmg, double-click and expect that all your files should be an exact copy of the original install files. And yet, sometimes, you get stuck with this message.

Here is a very simple fix that works 90% of the time: make sure that your post-install script can be executed!

Open a shell window, go to where your package is, and type:

chmod a+x yourpackage.pkg/Content/Resources/postinstall

Of course, replace ‘yourpackage,pkg’ with the package’s actual name.