Recently ran into this one myself - Just upgraded from an old Mosquito to a Vyper 2.
The serial port connection lead for the Mosquito does not work with the Vyper 2 (although it fits into the Vyper interface). Suunto have gone over to a USB connection lead and the latest version of SDM locates the Vyper 2 and puts it into transfer mode. There is no TR_PC option in the menu as it is now automatic.
You need to get the new lead and associated driver files to get this working. I got mine from a German guy who is selling them on ebay.
Rich