I had a similar problem on my Vista laptop
I called WD MyCloud Support at 1 800 275 4932.
The rep said there is a known incompatibility with the Java 7 Update 51. He advised that I uninstall 7.51, and download and install Java 7 update 45. I did this and also updated Vista to the latest service pack.
Now WD My Cloud.exe can open my shared folders, but it is really slow to open my music files (.wav). A 37 Mb file takes 2'30" to open.
I an connect through the web app, after bypassing a couple of security warning dialogues from Java. Again the download time is very slow.
NOTE: on my iPad MyCloud app, the download is almost instantanious.