At least I think this is related to filefield_paths.

The function node_export_file_alter_image has code like this:

$result = db_query(
      "SELECT f.*
       FROM {image} AS i
       INNER JOIN {files} AS f ON i.fid = f.fid
       WHERE i.nid = %d AND f.filename = '%s'",
      $original_node->nid, IMAGE_ORIGINAL
    );

That should look like this

$result = db_query(
      "SELECT f.*
       FROM {image} AS i
       INNER JOIN {files} AS f ON i.fid = f.fid
       WHERE i.nid = %d AND i.image_size = '%s'",
      $original_node->nid, IMAGE_ORIGINAL
    );

The filename field seems to no longer contain what Node Export is expecting it to contain. I think this change occurs when you install filefield_paths but I haven't deduced that for certain yet.