WD Backup Fail - Not enough space?

This problem may have been discussed, but I can’t find it exactly. There seems to be a lot of WD Backup Software failures. Mine is that I am trying to backup 2.1 TB of data on my WD Ultra 3TB USB Drive onto my 4 TB WD My Book. I have reformatted the 4TB My Book and it says it has 3.6 TB of space. When I try to backup 2.1TB of data from my Ultra 3TB, it says there is not enough space. Why not?

Hi okiejon,

Maybe you should try contacting WD’s Technical Support about this.

To Contact WD for Technical Support

https://support.wdc.com/support/case.aspx?lang=en
The link below will allow you to call support if you are having trouble with the form.