In Inventor 2014, trying to login to the Content Center using the "Content Center library read only user", you will get this message.
1) Create a Vault User account on the Vault Server with "Content Center Editor" role and with access to a Vault Database. Tell all users to use that account to log in to the CC Server. Note: if a licenced version of Vault is used for the CC Server, it will double the licence consumption. For this reason, use Vault Basic Server as the CC server. It is possible to detach the CC libraries from a Vault Workgroup\Professional 2014 Server and attach them to a Vault Basic 2014 Server
2) Dont "use separate server for content and Vault". Attach the Libraries to the Vault Server.
Development are aware of this issue, but because there is a workaround, its planned to be addressed in a future release.