Error on Build Ubuntu rootfs based on a prebuilt image of Armbian-Ubuntu-16.04, with LXDE desktop environment

Hi all,
I have reached at " Build Ubuntu Rootfs via a Pre-built Image ". I have chooses " Armbian_5.27_S9xxx_Ubuntu_xenial_3.14.29_mate_KODI_20170702.img ".
While i building root file system, Some errors are shown after executing the Step which is given below

"$ xdg-open archives/Armbian_5.27_S9xxx_Ubuntu_xenial_3.14.29_mate_KODI_20170702.img "

root@Cinesoft-Electronics-dept:/home/cinesoft/project/khadas/ubuntu# xdg-open archives/Armbian_5.27_S9xxx_Ubuntu_xenial_3.14.29_mate_KODI_20170702.img.xz
Warning: unknown mime-type for “archives/Armbian_5.27_S9xxx_Ubuntu_xenial_3.14.29_mate_KODI_20170702.img.xz” – using “application/octet-stream”
Error: no “view” mailcap rules found for type “application/octet-stream”
Opening “archives/Armbian_5.27_S9xxx_Ubuntu_xenial_3.14.29_mate_KODI_20170702.img.xz” with Disk Image Writer (application/x-raw-disk-image-xz-compressed)
file:///home/cinesoft/project/khadas/ubuntu/archives/Armbian_5.27_S9xxx_Ubuntu_xenial_3.14.29_mate_KODI_20170702.img.xz does not appear to be a regular file

(firefox:5975): GLib-GObject-CRITICAL **: g_object_ref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_unref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_ref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_unref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_ref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_unref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_ref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_unref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_ref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_unref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_ref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_unref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_ref: assertion ‘object->ref_count > 0’ failed

(firefox:5975): GLib-GObject-CRITICAL **: g_object_unref: assertion ‘object->ref_count > 0’ failed

Please go through the attachment.