I have a fresh iPhone project. When I "Build and Go":
Error from Debugger: Failed to launch simulated application: iPhone Simulator failed to install the application.
Why is that?!
You need to remove the folder as sudo ~/Library/Application Support/iPhone Simulator
sudo rm -Rfv ~/Library/Application\ Support/iPhone\ Simulator
It looks like previous versions of the SDK have some kind of permission trouble.
You don't have to sign code to run in the simulator, only for running on real devices.
Was the app running in the simulator successfully before? If so, did you make changes to the app since? Maybe try rolling them back until it starts working again to identify where the problem is.
Can other apps run in the simulator, or is the problem isolated to one particular app?
Take a look at this article.
Have you tried opening the simulator from /Developer/Platforms/iPhoneSimulator.platform/Developer/Applications/iPhone Simulator.app
and checking if anything (ie Mail, Safari, etc) works in the simulator? That'd tell you at least whether the Simulator is broken or there's something wrong with deployment.
I had this problem too! I deleted the folder "/Library/Application\ Support/iPhone\ Simulator" in my user directory. Started the simulator again and it started right up.
I ran into a similar situation where my home directory was on an NFS share. Deleting my "~/Library/Application Support/iPhone Simulator" directory didn't help, but sym-linking that directory to a location on my local disk did fix the problem.
I just solved this problem by reinstalling the SDK (iphone_sdk_3.1_beta_3__leopard) and restarting my machine.
After renaming the application the app would not launch in simulator. I was getting the above error. I tried most of the suggestions above, checked all my settings in the plist, also checked the build settings, and nothing worked. What worked for me was to reset the simulator.
try to "reset content and settings" on ios simulator menu
来源：https://stackoverflow.com/questions/591799/iphone-simulator-fails