Open Signed Offline/Developer Certificates are only available to users with a Publisher ID.
Developer Certificates will be ENABLED for users who have a Publisher ID ONLY
ONLY if you used a Publisher ID to create a .csr file with the DevCertCreate tool will you be able to use Open Signed Offline to create a Developer Certificate.
Developer Certificates are currently DISABLED for users without a Publisher ID. Users who DO NOT have a Publisher ID CANNOT request Developer Certificates or use Open Signed Offline.