In a small amount of cases, the publisher does not allow any version of the work being made Open Access (this is seldom the case, check Sherpa RoMEO for publishers’ policies on self-archiving).
If the publisher doesn’t allow you to deposit your article in a repository, the EC Open Access policy requires the author to contact the publisher. You are requested to inform the publisher of the EC Open Access requirements, and ask for an exception to the publisher’s normal policy to enable you to meet those requirements. It is important to obtain this permission in writing. A Template Letter (.pdf) is available that can be used when writing to the publisher asking for an amendment to your publishing agreement. When writing to publishers, it is better to write to the editor or officer in charge of authors' rights if possible, rather than to a general publisher's email address for permissions for re-use of published material. It is important that the request be seen as coming from the author and is part of the publisher/author relationship.