This message might shows up when you go to Tools > Demo Content Install ( http://d.pr/i/Mm93 )
If it's your case, it means that Zip extension is not enable on your server. To enable it, Go to your CPANEL > Select PHP Version and check ZIP. See Screenshot: http://d.pr/i/Nf7L
If you don't have access to your cpanel, please contact your webhost so he can enable Zip Extension.
2) Timed Out If you have a Timed Out message when you are importing the demo it means that your max_execution_time is set only to 30 second or so. Our demo's data is big and the import process while takes more than 30 seconds. It's why you see a timed out message. To raise the time a script is allowed to run, go to your CPANEL > Select PHP Version > Switch to PHP Option (http://d.pr/i/Z6ev)
Then check for max_execution_time and change the setting for 30 then click Apply and Save (http://d.pr/i/QXG2)
If you don't have access to your cpanel or you still receive a timed out message, please contact your webhost so he can set your max_execution_time to 600.
If above steps doesnt work, see solution 2 below:
*** SOLUTION 2 ***
Go to Appearance > Install Plugins. Install all required plugins and also, install the plugin “Iron Demos Importer” and make sure to activate them.
Download to your computer, the demo of your choice: