Above error messages comes up if your System reserved Partition (the one that windows installer automatically creates during windows OS installation) is too small to handle temporary files during backup.
The backup process is -> data goes to SRP -> data goes to external/network storage
The SRP needs at least around 100MB free space. Windows 10 by default creates only a 50MB partition, where windows already uses around 30MB of total space.
SRP can be extended with gparted or the free tool Partition Assistant from Aomei.