This error comes up when your server does not support unzipping files. It means that you have a Windows server without the php_zip extension loaded. Linux servers have built-in zip functionality. The only option if you want to be able to upload a zip file of images instead of one image at a time is to ask your host to install the php_zip extension.

If you maintain your own server, often you can enable the php_zip extension by editing the PHP.ini file. On many WAMP servers the line to enable php_zip is in php.ini, but simply commented out. The WAMP server from wampserver.com will allow you to turn on php_zip, or any PHP extension, by a menu choice from the tray icon.

If you cannot enable php_zip

If you are on a Windows server and cannot get php_zip enabled there is another option for uploading multiple files. You can FTP the JPG files to a subfolder of your ProofBuddy installation folder and select 'Server Files' on the add images screen. You can then browse to where you uploaded the JPG files and select them for addition.