It’s quite unusual to find a TV that has a genuine network file server access mode (yours might, though: what model is it?), so the chances are that you have been using twonky DLNA up to now… I’d suggest looking to see if your TV has upgraded its firmware.
As for the solution, you might check the ‘Navigation Type’ selected for your TV under Sharing|Media Receivers on the twonky UI pagepage; this determines the ‘views’ that are presented to DLNA clients. One of which is ‘By Folder’.
If you haven’t already seen it, this FAQ might help:
http://community.wd.com/t5/WD-My-Cloud/FAQ-Twonky-DLNA-Media-Server-Setup-amp-Use/td-p/858810
