This sounds like the device is dropping off the USB bus, which could be due to a known problem with the VIA USB 3.0 hub in the dock. There is a firmware update from VIA to fix this, and is available from the Toshiba support website here:
http://support.toshiba.com/support/m...eeText=3286829
Could you download and try this to see if it works?
Thanks
Wim