I am having the same issue on a fresh install of BE2012 14.0. When I test credentials it passes the "Microsoft SQL Server Instances" logon, but fails the MICROSOFT ##SSEE and MSSQLSERVER logons. All other backup jobs finish successfully including Exchange GRT backup.
I have tried checking the permissions, but every thing looks fine. I am a newbie to SQL, but did add an account in security (The one I created for this install of BE) and gave it admin rights to every checkbox and still the permission checks failed. I believe the default user for access was set to System Logon Account, but I changed it to the Domain Admin Account I used to set everything else up with and those credentials fail as well.
The job fails with the following error:
Unable to attach to <MYSERVER>\MSSQLSERVER.
V-79-57344-33932 - Unable to attach to a resource. Make sure that all selected resources exist and are online, and then try again. If the server or resource no longer exists, remove it from the selection list. Edit the selection list properties, click the View Selection Details tab, and then remove the resource.
Unable to attach to <MYSERVER>\MICROSOFT##SSEE.
V-79-57344-33932 - Unable to attach to a resource. Make sure that all selected resources exist and are online, and then try again. If the server or resource no longer exists, remove it from the selection list. Edit the selection list properties, click the View Selection Details tab, and then remove the resource.