Many others have had mkv stuttering problems with the last two firmware upgrades. Many of us have had to roll back the firmware to a previous version to get our systems to work the way they used to. For me, version 1.03.49 is the latest firmware without the stuttering problems. You do not need the network or the network adapter to do a firmware downgrade.
You can look here if you want to try rolling back your firmware.
http://wdc.custhelp.com/cgi-bin/wdc.cfg/php/enduser/std_adp.php?p_faqid=5800
Also, have a look at these threads that describe mkv stuttering problems.
http://community.wdc.com/t5/Networking/can-t-play-anything/m-p/118202#M5855
http://community.wdc.com/t5/General-Discussions/MKV-quot-stutter-quot-and-lag/m-p/118256#M18075
