Hi,
I had a similar problem as documented in this post…
http://community.wd.com/t5/WD-My-Cloud/MyCloud-4TB-Keep-losing-access-to-the-shares-daily/m-p/807497
This steps suggested by alex have worked for me and I went from the shares dropping daily to being stable for 3 weeks now.
I am using what was the latest firmware, v04.00.01-623. But there is a new version out now…?
Note: I am keeping my usage of the WD MyCloud very vanilla, only running the media service, no Mac/itunes stuff and no safe points, just the shares.