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 Push on refs/for/refs/heads/*)
if you bypass code review without Push access right on refs/heads/*
if you push an annotated tag without Push Annotated Tag access right on refs/tags/*
if you push a lightweight tag without the access right Create Reference for the reference name refs/tags/*
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