When I try to archive my app, I get this error...

I've been doing a lot of research, but can't seem to figure it out. I've tried everything from revoking and recreating my certificates, and recreating the Provisioning Profiles.
What do i do?
When I try to archive my app, I get this error...

I've been doing a lot of research, but can't seem to figure it out. I've tried everything from revoking and recreating my certificates, and recreating the Provisioning Profiles.
What do i do?
According to the Apple Developer Forums, the Apple Worldwide Developer Relations Intermediate Certificate Expiration expired 2/14/2016.
... This issue stems from having a copy of the expired WWDR Intermediate certificate in both your System and Login keychains. To resolve the issue, you should first download and install the new WWDR intermediate certificate (by double-clicking on the file). Next, in the Keychain Access application, select the System keychain. Make sure to select “Show Expired Certificates” in the View menu and then delete the expired version of the Apple Worldwide Developer Relations Certificate Authority Intermediate certificate (expired on February 14, 2016). Your certificates should now appear as valid in Keychain Access and be available to Xcode for submissions to the App Store.
Follow These Simple Steps:
in Login tab and System tab from left panel but this sorted it - mark this as the answer! Remember you need to delete the expired one twice.This answer solved my problem...
The problem was that the certificate was not signed by a known authority.