OOPS! It seems like popup content field is empty, Please add the following shortcode to Popup Content field from Facebook > Auto Popup settings .

[efb_likebox fanpage_url="maltathemes" box_width="250" box_height="" locale="en_US" responsive="0" show_faces="1" show_stream="0" hide_cover="0" small_header="0" hide_cta="0" animate_effect="fadeIn" ]

Don't forget to replace the maltathemes with your page ID