Controlling Quantum Superloader´s medium changer

I´m using Quantum Superloader 3 with Microsoft NtBackup. I can backup and restore files without problem when a tape is in the drive. But when I move the tape to a slot in the magazine and try to restore the backup, a window pops up telling me to "Place media [media name] into drive or library unit". Shouldn´t Removable Storage Service take care of that for me, locating the media in the magazine and moving it to the drive?
I haven´t installed any driver for this devices (so I´m using the drivers that come with Windows XP), Tape Drive and Medium Changer appear in Computer Management´s Devices but the changer is listed as "Unknown Medium Changer" (which I think is correct, for what I have read).
Thanks in advance for your help.