Your problem seems to have been solved only because you restarted your machine. But, it may crop up again. I just replied to someone else's post about this, so here it is...
That error will only occur if you start apache while logged in to the terminal. Sometimes when starting a daemon from the terminal, OS X will "forget" who started it and/or where. This will happen with daemons other than Apache, too. I've had the same problem with MySQL.
One solution is to make sure that the Apache daemon is being launched on startup, not from the Terminal.