Please check out these threads to see if they apply:
http://community.wd.com/t5/WD-My-Cloud/After-new-release-WD-my-cloud-not-accessible/m-p/820885/highlight/true#M24142
http://community.wd.com/t5/WD-My-Cloud/WD-My-Cloud-Not-Accessible-via-Host-Name-on-network/m-p/818795/highlight/true#M23929
http://community.wd.com/t5/WD-My-Cloud/My-Cloud-disconneted-itself-from-network/m-p/607675/highlight/true#M413
http://community.wd.com/t5/WD-My-Cloud/WD-MyCloud-Dashboard-kicking-me-out/m-p/777931/highlight/true#M19594
http://community.wd.com/t5/WD-My-Cloud/Firmware-v04-01-01-413-problem-with-scanning-of-wpl-files-still/m-p/831023/highlight/true#M25516