A step in an SSIS package failed - it was a file load and the load process was verified complete. We killed the process and it has been in Killed/Rollback for 13 days. The spid is not using any resources, but it does trigger alerts from our monitoring system(Spotlight).
While composing this we fixed it - so I'll post the solution for historical purposes. A .Net component threw an unhandled exception while running in an SSIS package. When I logged on to the server with /admin switch to kick someone off(both sessions were in use), I was presented with an error dialog. Once I clicked it away, the session disappeared.
This may be quite obscure, but may help another harried dba down the road.
John
SMBGuy