I download a sample of UICatalog and run it.When I compile it ,it shows the failed message:There is no SDK with the name or path \"iphoneos4.0\".I find the \"Base SDK\" of UICat
You have to make sure that you change to the "iPhone Simulator" under the project settings in the appropriate configuration (i.e. if you are building a debug build you have to change to the simulator under the debug configuration).
For some reason I was getting this error when I did change the simulator but realized that I was doing a debug build but changed to the simulator under the release configuration and not the debug configuration.