What options did you select to qualify for dropbox?
I am in a similar situation and it takes me to the payment page and schedule an appointment page.
I answered "Yes" to this question :
Are you traveling from another country to apply for a U.S. visa in Canada? *
Should I answer no for it? I am currently residing in the US , have a PR card and moving to Canada in Mar/Apr but want to get H1 visa stamped via dropbox in Canada in Dec/Jan time frame so I can make a trip to India.
I did answer it as yes, I am travelling from a different country from USA to Canada for Stamping as I am a Canadian PR I qualify for Visa Waiver and can drop the documents in Dropbox. I am still waiting my application status to change from No Status to Application Approved. Hopefully in a weeks time