It doesn’t look like you are using the correct form code.
Log into your Mailchimp account, select your List and then select to create a form.
Then select the Naked Form option and copy the form code you see.
Here is a screenshot https://www.dropbox.com/s/pmbrhct1odbmspq/mailchimp-form.PNG?dl=0
I just tried it with my account and it works, but you need to replace it with a form from your account.