I’m able to use the native.newTextBox object in the Xcode simulator (version 3.2.3). Have you tried removing the app from the iPhone Simulator and running the code? Does it still fail?
There does seem to be a problem with Corona builds for the Xcode (iPhone) simulator where the second time you run the program it either crashes the simulator or continues where it stopped (instead of starting from the beginning). We are trying to track down the problem.