My Provisioning Profile for my iPhone app expired, so I renewed it, downloaded it. Added it into Xcode. Manually added it to ~/Library/Mobile Devices. It would build and install onto the device, but when launched via the debugger I received the following output:
Error launching remote program: security policy error.
The app would terminate, the debugger was running but not attached to any process. The fix that finally resolved it was going to Settings > General > Profiles on the device and removing all of the expired Profiles in there. (Which were not related to the app in question.)