WD My Cloud Mac software can't access to WD MyCloud EX4 in Mac OS X 10.11 beta El Capitan

Hello there and welcome to the WD community.

Have you tried resetting the unit or perhaps rebooting the device? Here is a link that might help you with this:

http://support.wdc.com/KnowledgeBase/answer.aspx?ID=10432&lang=en