Plugin "Relocate Upload" errors

I am using the plugin, Relocate Upload so that I can move some uploaded files to a specified folder.

I get the following error when I move a file...

Warning: Illegal string offset 'sizes' in /home3/home1081/public_html/wp-content/plugins/relocate-upload/relocate-upload.php on line 56

Warning: Cannot modify header information - headers already sent by (output started at /home3/home1081/public_html/wp-content/plugins/relocate-upload/relocate-upload.php:56) in /home3/home1081/public_html/wp-content/plugins/relocate-upload/relocate-upload.php on line 73

Warning: Cannot modify header information - headers already sent by (output started at /home3/home1081/public_html/wp-content/plugins/relocate-upload/relocate-upload.php:56) in /home3/home1081/public_html/wp-content/plugins/relocate-upload/relocate-upload.php on line 74

...here is the relevant portion (I think) of the plugin php file...

    // attempt to move the file
    if(file_exists($new_path))
        $result="FAIL: move will overwrite an existing file";
    else if (rename($attachment_path,$new_path))
    {   $result="WAIT";
        // move any thumbnails too
        $pm=get_post_meta($id,"_wp_attachment_metadata", true);
        if ($pm['sizes'])
            foreach($pm['sizes'] as $size=>$pm_size)
                rename(dirname($attachment_path)."/".$pm_size['file'],dirname($new_path)."/".$pm_size['file']);

        // update the metadata to reflect the new location
        $pm['file']=$new_path;
        update_post_meta($id,"_wp_attachment_metadata",$pm);
        update_post_meta($id, "_wp_attached_file", $new_path);

        // update the post/attachment GUID field
        $new_guid = str_replace( str_replace(SERVER_DOC_ROOT,"",$attachment_path), str_replace(SERVER_DOC_ROOT,"",$new_path), $attachment_guid );
        $attachment_record = & $wpdb->get_row($wpdb->prepare("UPDATE $wpdb->posts SET guid='%s' WHERE ID = %d ", $new_guid, $id));

        // let the client know all is well, and what the new guid is
        $result="DONE: $new_guid";
    }

    header("HTTP/1.0 200 OK");
    header('Content-type: text/plain;');
    echo "$result";
    exit;
}

These errors only come up when I am moving a media file that is NOT an image file.