At this time the NASA OnEarch server has ceased operation. I’m not 100% certain that it is a permanent downtime, but it may be.
I am working on replacements, and will have a new release out as soon as I can.
What this means is that current copies of TopoFusion cannot download Elevation Data or Landsat tiles. You’ll get a “TF is having trouble contacting…” error.
Thanks for the patience, and stay tuned for further updates.