What does the production configuration look like in your database.yml? It looks like the user specified there is "deployer", which would be incorrect if the user in the cluster is "tasks" like you mentioned. If the username and password there is correct, I would start troubleshooting by trying to connect to the cluster via some other client - my personal preference is to just use the psql utility. You can connect like this (assuming psql is in your path) -
psql -h localhost -U deployer postgres
The "postgres" database is created by default in a new data cluster. Once you can get connected with a different client, update the production config in your database.yml with whatever changes are necessary and try again.