And Interface Builder starts up in the background but then stops responding? Have you recently changed your OS? Bought a nice, refurb iMac running Snow Leopard and transferred Xcode from an older machine running Leopard?
Me too.
It took me a long time to find the answer.
You need to get the iPhone SDK for Snow Leopard. Oh, and incidentally, there is a hint on the Apple Developer site (behind the login) because there are "Snow Leopard Downloads". Obviously I don't log in there every day, either.
