I am a registered Apple dev with the certificates, and mobileprofiles that i need. I have made several apps in xCode that I would like to test on my 3GS, I have registered my 3GS as one of my allowed devices but it still will not install giving the install prohibited error. The Xcode is set to same profile as my iphone has. Just dont kmow what to do. well i guess i =ll download sdk 4.1
You need to upgrade your SDK to 4.0.1 to use it with iOS 4.0.1 devices.
You will get this exact message if Restrictions are enabled on the device, specifically the restriction on installing Apps.
Is the iPhone OS Deployment Target in your Build Settings (either for the project or for the target) set for an OS version higher than the one on your 3GS?
来源：https://stackoverflow.com/questions/3653114/install-prohibited-iphone-sdk