The DELL PVT122T can use DLT IV tapes, LTO 1 and LTO 2. I believe you are out of luck with the LTO 3 tapes. There is not a driver update to install, that will let you write or read to the newer tapes. It is a physical limitation.
It goes the other way too. I am currently using an LTO 4 autoloader, it can write to LTO 4 and 3 tapes, but I can only READ LTO 2.