What about the plain, vanilla native windows backup?  Does it let you back to tape?   Depending on what happens you'll either have a bug with Symantec, which you can then log a call on, or a program that has nothing to do with symantec, so at least you can start focusing on likely faults.

Also, when you say the controller "sees" the tape .. this is hardly verification that it is operational.  I would personally download an ubuntu live CD or USB, boot the ramdisk version of linux, then try copying something, and restoring from a scratch tape.  This will tell you that the hardware is 100% good if successful.

Ubuntu will auto-discover the tape, so when you get to the prompt (Boot the CD, don't install it to your HD, all this happens in RAM, feel free to unplug power to your hard drives during this, for safety if you are unsure about LINUX)

anyway,    go to the terminal prompt, and enter;

tar cvf /dev/rmt/0m /usr

Above will copy all files from /usr and copy them to tape.
Once complete ..  enter

tar tvf /dev/rmt/0m   (And this will give you a directory listing as it reads through the tape)

What is the SCSI interface you are connecting to? It isn't part of the RAID controller is it? That is a common mistake and is not supported.

You could also check the BE logs to look for device errors:
Program Files\Symantec\Backup Exec\Logs\adamm.log

Why i'm saying it 'Sees' the tape drive is because of what you are seeeing in my screen shot. Somehow my system knows that it is an Ultriam 2 tape divise that i am trying to connect. (although it had once worked with this box in the past - maybe it has a store on info telling it that was what was connected in the past). Windows backup does not seem to see the tape drive. When setting up a backup, i only get the 'Select Destinatioon Disk' prompt - not any reference to a tape drive.
i will try the ubuntu now.

Well, then I would boot that system to LINUX and actually read/write to the tape device.  Let's determine whether it is a hardware/connectivity problem first.  Too many unknowns so it is rather inefficient to waste time looking at windows drivers and application software if all we have to go on is what very well could be stale registry data.

There are commercial products for a few hundred bucks you can use to test/configure tape drives from inside of windows, but just loading linux on a ramdisk to read/write to the tape for free is better.  If the tape drive acts up or performance is bad, then it is the time to start looking at test software perhaps.

the hardware tree which the driver install references is probably the Windows hardware device map which is displayed via the Device Manager, right click on My Computer Manage. It should show up there under Tape Drives or other if the device is not identified. You can try installing the generic MS LTO driver just to see if that works. Device Manager right click on the drive, update driver, browse my computer, then Let Me Pick and the driver will just be listed as "LTO". If the drive does not show up in the Device Manager at all then check the Event Viewer System log also under Manage for possible messages relating to it. In addition Quantum has its own diagnostics that might be a good idea to try out.
http://www.quantum.com/ServiceandSupport/SoftwareandDocumentationDownloads/LTO-2Drives/Index.aspx

the hardware tree which the driver install references is probably the Windows hardware device map which is displayed via the Device Manager, right click on My Computer Manage. It should show up there under Tape Drives or other if the device is not identified. You can try installing the generic MS LTO driver just to see if that works. Device Manager right click on the drive, update driver, browse my computer, then Let Me Pick and the driver will just be listed as "LTO". If the drive does not show up in the Device Manager at all then check the Event Viewer System log also under Manage for possible messages relating to it. In addition Quantum has its own diagnostics that might be a good idea to try out.
http://www.quantum.com/ServiceandSupport/SoftwareandDocumentationDownloads/LTO-2Drives/Index.aspx

Command line with Ubuntu says: "cannot open: No such file or directory"

It turns out that this was a SCSI adapter problem, but thanks for all the input.