Duplicate large mkv files when browsing DLNA server....aaaaaaaaargh!

Hi All,

I've recently bought an Asus RT-n56u router to allow me to have an external HD plugged in so I can stream video to my Samsung C8000 TV over wifi. 

The box is essentially a DLNA server but as this is my first time using one I cannot figure out one annoying bit...when I browse the folders from my TV or windows 7 machines as DLNA/media devices the larger 1080p mkv files (around 10Gb) seem to show up twice in their respective folders and I can play either one of them.  However, when I view them on a usb stick directly in the TV or as a network drive from a laptop then there is only the one file which is as it should be...if anyone knows the answer as to why this is happening please please help me out as it's driving me nuts.

Many thanks,

Franklioni

PS if this is wrong channel to ask...