Firmware upgrade is a reliable way to break the Twonky media server.
You might gets some tips on how to recover the situation, and how to prevent it happening in future from my FAQ:
http://community.wd.com/t5/WD-My-Cloud/FAQ-Twonky-DLNA-Media-Server-Setup-amp-Use/td-p/858810
One common problem is that you may need to re-enable Media Serving on the Public Share; this can be turned off by a firmware upgrade, and it’s one of two controls you need to set to enable media streaming.
