Hi Erling strand .
You can to try checking the disk functionality... also the correctness of the destination directory... and the capacity of the available space, via a terminal connection to the set-top box (ideally using the PuTTY application, via SSH or Telnet protocols).
I don't know what you're doing wrong. Maybe you used a dot instead of a slash (you have to use a slash at the beginning of the path). Maybe there's a wrongly named, created directory on the disk (i.e. the directory doesn't exist - with the wrong name). You need to check more things and verify them. You can also verify with an FTP connection to the set-top box, where you check for the existence of the directory in the target path.