Earlier today, I was struggling to diagnose a T-SQL job that selects info from a master db table and sends them to an email. I kept getting SELECT permission issues in the error message. I didn't realize that jobs don't always run as the job owner and it was running instead under the SQLServerAgent account, that wasn't setup as a login on SSMS. As soon as I added the SQLServerAgent account it started working just fine.
This was the only job that was all T-SQL rather than PS or CMDExec, so none of my other jobs were failing.