If your Mac is using El Capitan there are a variety of issues that are discussed in numerous other threads. One can use the forum search feature to find those threads. Try using the IP address rather than “wdmycloud” to access the My Cloud.
Here are a varity of threads that may assist.
How to access the Dashboard on a My Cloud device: http://support.wdc.com/KnowledgeBase/answer.aspx?ID=10420
https://community.wd.com/t/support-os-x-el-capitan/96744
https://community.wd.com/t/cannot-acces-mycloud-with-mac-yosemite/138060
