Rails and PostgreSQL: Role postgres does not exist

Question

I have installed PostgreSQL on my Mac OS Lion, and am working on a rails app. I use RVM to keep everything separate from my other Rails apps.

For some reason when I

Answer 1

This message pops up, when the database user does not exist. Compare the manual here.
Multiple local databases cannot be the explanation. Roles are valid cluster-wide. The manual again:

Note that roles are defined at the database cluster level, and so are valid in all databases in the cluster.

You must be ending up in another database-cluster. That would be another server running on the same machine, listening to a different port. Or, more likely, on a different machine.

Could it be that the message comes, in fact, from the remote server?