Safe Point Warnings and Failed Backups

I have  the same  error when using a  usb 3.0 disk as safe point. Formating the USB  disk to ntfs or FAT32 do not solve the problem.   It looks like the backup are almost finished (take several hours) . My 4tb wdmycloud has the latest firmware.

I know I’m a little late to the party on this but I’m having the same issue of not being able to create a safepoint.  Just wondering if a solution was found?

I have a 4TB WD Elements external drive connected to the 2TB Mycloud with the lattest firmwar

Is there anything specific/formating wise that I need to do for the Elements drive?

I was hoping to use the Elements drive to backup the Mycloud using safepoint and backup a 500G laptop and 250G netbook using Windows backup.