The WDTV Play uses “Media Shares” using DLNA Compliant Software (eg. Twonky, TVersity etc)
Page 24: http://www.wdc.com/wdproducts/library/UM/ENG/4779-705073.pdf
“Network Shares” are not supported on the WDTV Play
(The WDTV Live / WDTV Live Hub / WDTV Live Streaming (SMP) support both Network Shares and Media Shares)