Rake Aborted! “Don't know how to build task 'dropbox:authorize'”

Working with rails and my application, and bumped into a problem. I’ve
to the step where I need to install dropbox, and incorporate it to my
The first step was to install the dropbox gem, and that happened with
Then I had to complete the migration, which was also a success. Then it
came to the problem to rake dropbox, which the problem happened.

This is the code that I put into my command line:

rake dropbox:authorize APP_KEY=your_app_key APP_SECRET=your_app_secret
ACCESS_TYPE= dropbox

Of course I put my key and secret code into the code, but when I pressed
enter, I got the following error.

rake aborted! Don’t know how to build task ‘dropbox:authorize’