It sounds like the Toshiba drive may have gone into sleep mode:
http://www.csd.toshiba.com/cgi-bin/tais/support/jsp/bulletinDetail.jsp ?soid=2632875&pf=true
Suggest doing 1) above, and 2) allocating a permanent Drive letter as described at the first link I provided, and 3) then update the new driveletter/folder location in LR.