Problem solved with the help of Veeam support.
The drivers for the tape library weren't installed, so Veeam couldn't see it. The official "Overland way" says to install the IBM drivers. The program tells that the library is also installed, but it isn't...
Asking Google lead me to this:http://catalog.update.microsoft.com/v7/ ... 50578ec73c
Installed the drivers and everything is fine!
Thanks to you, have a nice weekend!