But SQL Server Agent is a Windows service. That means it runs under the context of a Windows user account or the LocalSystem. If it's running under LocalSystem and you've removed BUILTIN\Administrators, you'll need to add [NT Authority\System] as a login and put it in the SysAdmin role.
You can find what account SQL Server agent is running under by Start | Run | Services.msc. Scroll down to where you see the service.
K. Brian Kelley
http://www.truthsolutions.com/
Author: Start to Finish Guide to SQL Server Performance Monitoring
http://www.netimpress.com/shop/product.asp?ProductID=NI-SQL1
K. Brian Kelley
@kbriankelley