64 bit operating systems are best supported in Logger Pro 3.8.3 or newer. If you have an older version of Logger Pro 3, the update is free from:
http://www.vernier.com/tech/lpupdates.html

Both the OHAUS balances and the Watts Up Pro use a device driver that uses serial communication protocols on a USB port. Sometimes, when you go into the connect interface menu, the COM port that the device is attached to will not show up for that interface. The same COM port will show up on the connect interface menu for other devices.

There are odd interactions between certain version of Logger Pro and the certain versions of drivers. Go into the Device Manager and looking at the date of the driver for the “USB Serial Port.” If it says 7/12/2010 then you need Logger Pro version 3.8.3. (3.8.0 and 3.8.2 will work with older versions of the driver.)