You have to firstly check to see if the USB drive is correctly identified in Windows. Simply open This PC and expand the drives list. After this procedure, open Memorex ExPressit Label Design Studio and when you want to open something, make sure to select ALL FILES else the software will look only for the supported files, which I believe is the cause to your issues.
I know it happened with one of my programs when it didn't allowed me to open other files unless the ones supported by default.