Xcode can build a project but can't run it on simulator

Generally, if you can't Run a project, either:

• It doesn't have a build scheme that knows how to "run". Check at the top next to the Run/Stop buttons that there's a profile name and target device shown. If the box says No Scheme then click on it and create a New Scheme. If there IS a scheme, click on the drop-down menu (left divider in Xcode 4.2+, anywhere on the box otherwise) and go to Edit Scheme to make sure the scheme was set up correctly for Running

• It doesn't have a build configuration set. You should see this in the Run section of your build scheme. Check there's one selected. If the list is empty, go to the Project icon at the top of the leftmost pane, select the Project, go into the Info section, and create a build configuration, although there should already be at least one if you can build the project

• It doesn't have a runnable target at all, which might mean you've got a project which compiles to a static library or framework for use in OTHER projects. If this is the case, you should see the icon for your build Target as a yellow toolbox (framework), or a little white building (a "library", although to me it looks more like the United States Supreme Court Building).

• The target isn't valid for the Simulator, which means you might need to add i386 to the list of Architectures and Valid Architectures on the Target before you can run it

• The target isn't valid for the currently connected device. For this one, check the Deployment Target number is set back enough to be valid for the device's version of iOS

• Xcode can't see the connected device. Try unplugging and plugging it back in. If it still doesn't recognize it, you may have not added it to Xcode (Window -> Devices -> Select the device -> Use for Development)

Make sure that in your Edit Scheme (click on your project name next to stop button -> Edit Scheme), in the Info tab of the Run menu selection, that your .app is selected as the Executable. I had this issue and "None" was selected, happened after refactoring the project's name and reconfiguring the build targets.

you may download a project that the deployment setting (the ios version) is higher than the one your xcode support. if this is your situation, you has two options to sovle the problem.

1. try run the project in a older deployment option. follow these instructions (if the project just setting to a higher version but not using any feature of the higher version. this approach should work):select project file in xcode > select the target you are going to run > select summary tab > in section 'iOS Application Target' > in the combo box about 'Deployment Target' select the version that your Xcode support. and then you could select and run the project in the simulator.

2. if the project dose use features in the higher version, then you should update your Xcode in order to run the project.

Hope this helps!