"cannot open" or "unknown object" when training coco

[shinandrew]

I've modified CONFIG and main_cls.lua as necessary,
and ran train_coco.sh.

I got a bunch of outputs that look like following:

/home/ms_coco/train2014/COCO_train2014_000000035230.jpg
/home/ms_coco/train2014/COCO_train2014_000000163761.jpg
/home/torch/install/share/lua/5.1/torch/File.lua:375: unknown object
/home/ms_coco/train2014/COCO_train2014_000000058429.jpg
/home/ms_coco/train2014/COCO_train2014_000000198382.jpg
/home/torch/install/share/lua/5.1/torch/File.lua:375: unknown object
/home/ms_coco/train2014/COCO_train2014_000000212091.jpg
/home/ms_coco/train2014/COCO_train2014_000000215679.jpg
/home/torch/install/share/lua/5.1/torch/File.lua:375: unknown object

or

/home/ms_coco/train2014/COCO_train2014_000000178793.jpg
/home/ms_coco/train2014/COCO_train2014_000000183212.jpg
cannot open </home/ms_coco/train2014/COCO_train2014_000000498615.jpg> in mode r at /tmp/luarocks_torch-scm-1-3096/torch7/lib/TH/THDiskFile.c:649
/home/ms_coco/train2014/COCO_train2014_000000498615.jpg
/home/ms_coco/train2014/COCO_train2014_000000246971.jpg
cannot open </home/ms_coco/train2014/COCO_train2014_000000220148.jpg> in mode r at /tmp/luarocks_torch-scm-1-3096/torch7/lib/TH/THDiskFile.c:649

I've check many times that the path is correct and the files exist.
What could've gone wrong?
If everything goes right, what kind of print output should I be seeing?