Not enough room for files

Are you using Windows or Mac?

If Windows, there is bug in the Microsoft WebDAV protocol that can cause the MBL to only show as the size of your C:\ when mapped as a drive to Windows, and could cause this error. 

There is a very helpful guide written by another contributor to this forum that explains this in detail and how to solve it:

http://community.wd.com/t5/My-Book-Live/WebDAV-Primer-Microsoft-vs-WD-My-Book-Live-etc/m-p/576975/highlight/true#M23535