So what exactly do you want to know? :-) To me it seems like you have answered all your questions yourself.
I had a user get this error when he executed the "Move To" command in the context menu. In the docs it says it can be a myriad of things, including permissions. After I did some trussing on a solaris box, I noticed that WinSCP was trying to hardlink the files across partitions or devices as the source and destination were on different partitions. How does WinSCP execute the operation when "Move To" is called. The "Move To" command appears to be local (meaning from a dir on the remote system to another dir on the remote system) while move is from the remote to the local system. Any further insight would be appreciated.