I cannot register my Snuza Pico.

A Snuza Pico can only be registered to one username. If you bought your Snuza Pico second hand please contact the previous owner of the Snuza Pico and request that they deactivate the Snuza Pico by logging in with their username at connect.snuza.com and clicking on the red de-activate button at the bottom of the page.