import the developer certificate and add it to the key check Export and import help and profiles and the apple troubleshooting page
apple documentaion says
If the certificate already exists in the Member Center, the "Your account already has a valid certificate" dialog box appears. This usually happens when you move from one Mac to another. If possible, export your certificates as a developer profile file on another Mac and then import them onto a new Mac, as described in the “Export and Import Certificates and Profiles” section. If you do not have a backup of your developer profile, click the "Feedback and Request" button when the "Your account already has a valid certificate" dialog box appears.
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