Copy Data to external HDD

[dahspeataerchaen]

I tried to copy data to an external HDD.
Unassigned devices and unassigned devices plus is installed.
There is no problem copiing fron the HDD to the Array.
I tried it with the file Manager, krusader etc. but the answer is always the same: Invalid target Enter a valid traget.
in the file Manager the external HDD adress is: /mnt/disk/externalHDD
It just does not work.

Any ideas?
Sreenshot of Unassigned devices Settings:
Thank you for you help.

Peter