Before MI3.5, the second-generation VT DSOs support USB 2.0 High Speed Only. From MI3.5 onwards, USB2.0 High Speed, USB2.0 Full Speed and USB1.1 Full Speed are all supported automatically. USB2.0 High Speed is preferred especially in streaming mode of the oscilloscope and signal generator as it allows higher sampling rates to be used for continuous streaming, while USB Full Speed allows the use of a USB full speed isolator which is critical if you are not doing floating measurement. So far, there is no USB2.0 High Speed isolator in the market.
If you install the VT DSO driver before, you need to remove the old driver and then install the new driver. Please refer to:
http://www.virtins.com/Upgrade.shtml on how to update the VT DSO hardware driver.