Playing MKV files via NAS

Hi guys

I have a 3td WD Mycloud & am trying to stream MKV files to TV

I have a PS3 & can successfully point PS3 Media Server to the NAS drive via PC & play the MKV’s OK

BUT if I point PS3 Media server direct to NAS drive (PC turned off), I get a message of unsupported data on PS3?

Any ideas?

The PS3 doesn’t support MKV.