I have recently completed an erase and fresh install of OS X and applications including Xcode.
I can build & run any app to the iOS Simulator (6.1) without issue. I cannot however build and run to a device, although I could do this prior to the reinstall. Instead I receive the following error under the heading...
Check Dependencies
Code Sign error: The identity 'iPhone Developer' doesn't match any valid, non-expired certificate/private key pair in your keychains
I have a valid and current iOS Development account.
I have refreshed my provisioning profiles. Yes I have done some reading, although I am still to understand how these work, so the answer may be locked up in that somehow. (I am new to Xcode and Objective C and have been focussing on the code.)
Hoping someone can help?
Also note that after five years my Time Capsule broke (power supply I suspect) before I could completely restore selected directories, so I am unable to go digging around in my old Library directories for files that might help me now.
You did a reinstall of your system, so you lost your private key and your certificate that was stored inside your keychain. If you don't have a export from Xcode as backup then you need to request a new key and make new certificates:
It is worth looking in the best practise guide: App Distribution Guide: Best practices