There is not enough space on disk, but there IS!

I purchashed a 4TB My Book external drive to back up my Dell Inspiron 15" laptop running WIN 8.1.  I’m running the lastest version of the WD SmartWare software to automatically back up the drive.  It very quickly backed up most of my C drive (917 GB), but for some reason, it has stalled on the last 116 files (93 GBs).  For all of these files there is an error message - There is not enough space on the disk.  The WD software is showing 1.7 TBs free, so I’m not sure why it won’t back up the remaining files.  The My Book is formatted as NTFS and none of the remaining 116 files are larger than 4GB, so it is not the FAT32 problem that others have encountered.  This is very frustrating, because most of these are video files which are the exact files I wanted backed up.  If anyone has anysuggests on how to remedy this problem I’d greatly appreciate it.

Welcome to the Community.

Is this happening on different computers using WD SmartWare? Does this happen after the hard drive has been idle/inactive for a while?