This is a general error message that is returned by Gerrit if a push is not allowed, e.g. because the pushing user has no sufficient privileges.
In particular this error occurs:
if you push a commit for code review to a branch for which you don’t have upload permissions (access right +2 Upload permission in the Read Access category)
if you bypass code review without sufficient privileges in the Push Branch category
if you push a signed or annotated tag without sufficient privileges in the Push Tag category
if you push a lightweight tag without the access right +2 Create Branch for the reference name refs/tags/* in the Push Branch category
For new users it happens often that they accidentally try to bypass code review. The push then fails with the error message prohibited by Gerrit because the project didn’t allow to bypass code review. Bypassing the code review is done by pushing directly to refs/heads/* (e.g. refs/heads/master) instead of pushing to refs/for/* (e.g. refs/for/master). Details about how to push commits for code review are explained here.
Part of Gerrit Error Messages