Hi Heku,
When you create a Campaign, it automatically has a dependency on workflow rights, as a Campaign usually would not exist without a workflow. That said, if you are trying to prevent users from sending deliveries, you could ensure that their Start Deliveries and Prepare Deliveries rights are removed. This will prevent desired users from approving or sending any deliveries.
That said, the Workflows right would still be required to resolve your error.
Regards,
Craig