I am having the same issue. I currently have a 4Tb TeraStation II Live HS-DHTGL/R5 ver 2.14 and I am having issues running a normal backup to a 8Tb LinkStation LS-QL F/W 1.11.
The backup seems to run fine for ~20 hours and then it suddenly stops however on the TeraStation it says that the backup is still in progress but no data is being copied over. It usually stops at ~ 160Gb. There is more then enough room on the link station.
Using copy and paste with a laptop or workstation does not seem effected however I should not have to leave a computer on to do this when the functionality should work on the TeraStation.
Any thought or ideas about this issue?