Been there - done that.
Make sure your certificate is in the "login" keychain, and that that i the default keychain (highlighted bold) in Keychain Access
Make sure you have both the private and public keys for your certificates and that they are valid. You will also need the Apple Worldwide Developer Relations Cert Authority installed.
I assume you have dragged the profile into xcode - easiest to drop them onto the xcode icon on the dock.
Make sure as Paul says, that the bundle identifiers all match up
You say you checked the certificate in the distribution configuration. Its not the certificate you need to concentrate on but the provisioning profile.
Select your Release config top left, click on the project under groups & files and do cmd I. Select build tab and then pick distribution in the top left. Then look at the Code Signing Identity. Pull down the dropdown list and make sure you have the right application identifier, the right profile and the right certificate. Don't use the Automatic Profile Selector.
Hope one of those steps helps!
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…