I'm having that same problem, and from various forums it seems far too common for PerSonus to not provide an answer. My first song exported perfectly to a wav. My second song, with all the same settings, creates a file that is the right length but is completely silent. I've watched videos, looked through several forums, checked all settings and followed all steps. Nothing is helping.
This software is created for making music, not for entertaining engineers. And when a problem like this disrupts the work flow it plays hell on personal creativity. I don't want to sit around all day dicking with this. I'm doing what it says should be done, it's not working, and only other users with the same problem are offering suggestions but unsuccessfully. Hey, PreSonus, do you even read these issues?