I'm not sure Bob ...
I would suspect that it may have something to do with MEGA imaging and CHIRP frequencies not being supported by Humviewer ... Martin (Humviewer creator) has not checked into the forum in a few years now and no one knows how to contact him ...
I would also suspect that if you set your HELIX to fixed frequencies by turning all CHIRP off - then Humviewer may work with your recordings ...
Rickie