Hi,
I can confirm this is a bug in the most recent release. To fix it manually, please try the following:
1. Make a site back-up, just in case
2. Open up the wp-content/plugins/ajax-search-pro/includes/functions/functions.php file on your server via FTP/SFTP
3. Replace it’s contents with this
4. Save the file
Refreshing the page and trying again should resolve the issue.