Failed to launch simulated application: Unknown error

Question

• OS X 10.5.7 (genuine Mac)
• Xcode 3.1.3
• iPhone SDK 3.0

When I try to execute my iPhone application in simulator, I get the dreaded error

Answer 1

Another reason for such an error message: a number in the executable file name (set in the projet plist file under "Executable file" key). The solution was to remove any number there, remove the application in the simulator, quit and relaunch xcode, rebuild, and tada, it's that simple :-(