Thank you for the details. I was not able to log-in to the back-end with the details, but on FTP I am seeing a very old version of the plugin installed, over 2 years old.
Please make sure to remove the old version, and update it to the new one first. It will very likely resolve any issues.
Thank you! The issue was the server memory limit. Activating any more plugin was causing the problem (not only the search), as the server was running out of memory. I have placed the following line to the wp-config.php file in your root directory, to allow more memory for the WP process: