Xcode iOS Development signing identity

I have a problem getting a iOS Development signing identity into Xcode. I have tried loads of things to get it working but I keep failing.

I have went the automatic way and let Xcode do it all but I kept going in circles where Xcode kept saying:

No signing identity found. Xcode can request a new iOS Development signing identity for you.

Followed by:

Your account already has a valid certificate. If you have your signing identity on another Mac, you can import a developer profile. You can also revoke the current certificate and request one again.

I have done many steps:

• Removing my account from within Xcode's preferences.
• removing everything from the key chain app.
• clearing everything from within the developer member center (apple developer website)
  • removing all provisioning profiles
  • removed my device
  • revoked all all my certificates
• restarted Xcode to perform a 'Clean' project from the Product menu.
• even went into my project.pbxproj file to clear anything related to PROVISIONING_PROFILE
• removed all provisioning profiles from my device.

After this I went back into Xcode:

• added my account into the preferences section
• clicked View Details
• did a refresh
• Xcode automatically creates two certificates
• Xcode automatically creates provisioning profiles
• Xcode only creates a single Signing Identity: only for iOS Distribution. This is my problem: I can not get an iOS Development signing identity.

After not getting it to work I went the old fashion manual way:

• first clearing everything like the above
• created new certificates manually, downloaded them and added them to the key chain app.
• created new provisioning profiles manually, downloaded them and dropped them onto the xcode app icon. At the end the result is the same; When I am in Xcode > preferences > accounts > view details:
• I do have a distribution signing identity
• I do NOT have a development signing identity

When I click the + button under the Signing Identities and choose 'iOS Development' nothing happens..

I have found lots of posts here on StackOverflow, I tried their suggestions but it won't work for me. Examples of other posts: here, here and here

I am working with the latest version of Xcode: 6.2. I am working on an app which is already in the App store.

Edited: I have also changed the code signing build settings of my project and target into Don't code sign and put it back to iOS Distribution for ad-hoc and iOS Development for Debug.

Together with a very helpful person on the Apple Developer forums we have tried to figure this out.

I was so blinded by it not working, it never came to mind to try out and build another project and to see if that would work. I was completely focused on my certificates and profiles within the member center and my account details within xcode. When I did try to build another (random) project, it worked in one go. This told us it must had something to do with the Build Settings of that one specific project which xcode could not code sign.

At the end, in xcode I went to the Build Settings of my Target. Within the Code Signing section I changed the values of Any iOS SDK to point to a specific Identity in my Keychain instead of having them on automatic (iOS Developer / iOS Distribution). This fixed my issue and I was able to build/deploy to my device and I was able to upload a new build to iTunes Connect.