You are on to something. I have no clue what it means except that it seems to be some corrupt Jpeg data. I'm not sure, I I export from LR always the same way.
Here is what it says on the error log
home2/ottomoto/projects/nume/releases/20121111192110/lib/util/extend_string.rb:58: warning: encoding option is ignored - U
[16-Sep-2013 14:09:29] PHP Warning: imagecreatefromjpeg() [function.imagecreatefromjpeg]: '/home2/keracerv/public_html/wp-content/upLoads/p4/images/masthead_image7_1379340569.jpg' is not a valid JPEG file in /home2/keracerv/public_html/wp-content/themes/prophoto4/classes/class.gd.php on line 56
[16-Sep-2013 14:09:29] PHP Warning: imagecopyresampled(): supplied argument is not a valid Image resource in /home2/keracerv/public_html/wp-content/themes/prophoto4/classes/gdModify.php on line 197