I had the same problem - I found that it was because there was no password set for the user even though a password was set for the account…it sounds complicated. Log in to the WD My Cloud Web Interface on your desktop browser (
http://WDMyCloud
) and under users check to see if the password option is toggled ON (under USERS). In my case it wasn’t, but when I specified a password for the user it worked on my Galaxy S5:
