OpsMgr (SCOM) - Ghost Agents

They show up in Monitoring views, but not in Administration ?
Well ... no problem!

At OperationsManager Database :

 -- #1  
 SELECT * FROM dbo.[BaseManagedEntity] where FullName Like '%Windows.Computer%' and Name = 'your_host_here'  
 -- #2  
 UPDATE dbo.[BaseManagedEntity]  
 SET IsDeleted = 1   
 WHERE FullName Like '%Windows.Computer%' and Name = 'your_host_here'  

Hope it helps you out.

Cheers,