What I did was change the certificate type to one of the Developer ID Installer type:
Go to developer.apple.com/account, and click on Certificates, IDs & Profiles.
In the sidebar, select OS X from the menu, and under Certificates, select ALL.
Click on the (+) button at the top right.
Select Developer ID under Production, and click Continue.
Select the type of certificate -Developer ID Application or Developer ID Installer- and click Continue.
Follow the instructions to create a "certificate signing request (CSR)" using Keychain Access, and click Continue.
Click on Choose File.
Select a CSR file (with a .certSigningRequest extension), and click Choose.
Click on Continue.
Click on download (Download).
EYE: Only the Team Agent can create this type of certificate, if not
You are the Team Agent, even if you are an Admin user, you can not create it,
communicate with your Team Agent and send your CSR file so you can
generate the certificate.
Once this is done, double-click the certificate (previously downloaded) to add it to Keychain Access and proceed to sign your .pkg with the productsign (1) tool as follows (Terminal):
productsign [options] --sign identity input-product-path output-product-path
productsign --sign "Nombre de tu Certificado en Keychain Access" ruta-de-entrada-al-pkg ruta-de-salida-al-pkg