No idea there DNJ sorry to hear it.
My 1gb and 512mb USB drives are USB2 but still work with the Tyros 2.
I know different memoty sticks operate at different speeds but I wouldn't have thought that mattered, unless it's too quick for the T2 to cope with or is that just daft on my part?
Have you tried both USB ports on the T2 to make sure it's not just the front or rear at fault?
Good luck m8