Does the Sql Server Agent account need sysadmin permission?
Further to Shawn's answer, the Books Online topic titled Select an Account for the SQL Server Agent Service also says:

The account that the SQL Server Agent service runs as must be a member of the following SQL Server roles:

The account must be a member of the sysadmin fixed server role.

To use multiserver job processing, the account must be a member of the msdb database role TargetServersRole on the master server.