We had some trouble running the full backup (both from CA and stsadm), we got error messages in CA that said “Error: Object SharePoint_Config failed in event OnBackup. For more information, see the error log located in the backup directory. SqlException: Cannot open backup device…” and in EventViewer it complained that we used a Bad username or password. Started to investigate that the app pools ran with the right userid = ok, services on the sharepoint server = ok, user account that initiated the backup = ok, network share had correct permissions and that it actually was a share = ok, the app pool account/service accounts/backup account had right permissions on the SQL server = ok, and then I thought everything was checked. But not. Turns out that the MSSQLSERVER service on the SQL server was running on a local account and that account tries to access the file share where you want your backup files and that share is of course not on the same machine so – access denied for that local account! It’s all so clear when you find the error, isn’t it? 🙂 So, we changed the MSSQLSERVER to a domain account which has all rights to the network share and the databases, and now our backup is up and running!