Sometimes Pulse can get into a strange state where it gets a corrupted thumbnail image, and then the thumbnails requested after that are also corrupted. This is an issue we're working on (it seems to be worse for some phones than for others), and for now we recommend trying to request a few thumbnails to clear things out, or quitting and re-opening the app.
There are a few other reasons that we have found that can result in thumbnails coming back corrupted, or not at all.
Make sure the cable from Pulse to your phone is connected securely. Try reconnecting the cable to Pulse and your camera, and restarting both devices.
Make sure your camera's battery is well charged
Some cameras (especially Nikons) have to be put into a special mode to enable USB tethering
We have seen that Pulse can have issues retrieving thumbnails on cameras that have multiple card slots. It is possible that if you have a camera with multiple SD or CF cards in it, that Pulse is pulling from the wrong one, which may be empty. Please try only using one card, or saving to a different card. If this fixes the issue for you, please let us know!
Still stuck? Shoot us an email. We're here to help.