There could be a situation where the password on the account used to log in to the database has changed but the registry password has not. This can be corrected by referring to the article, Changing the vCenter Server database user ID and password, found at http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1006482.

Authenticating the database could be a problem if you have imported an instance into the database from another. In this case, the Microsoft article How to transfer logins and passwords between instances of SQL Server, will be helpful, which can be found at http://support.microsoft.com/kb/246133.

If, for whatever reason, the user was not granted permission to access the vCenter database, the administrative credentials required for Oracle and SQL Server databases when installing or upgrading the vCenter Server article should help. This can be found at http://kb.vmware.com/selfservice/microsites...