I had the same freaking error when installing service pack4. I went through the services and sorted by status and what was started. I noticed service pack service wasn't enabled, nor was my remote procedure call and workstation, I enabled these and a couple other misc services (such as event viewer) and it installed.

I was getting "Unable to register the event source."
"unable to conenct to metabase"
and "setup failed to remove ism.dll script mappings. Service pack will abort setup."

__________________
Don't panic, the panic button is the red one.