When switching to Yosemite I did a clean install of my Mac and now I'm having issues submitting my iOS to the store.
When I validate my archive I keep getting "Your account already has a valid iOS Distribution certificate".
I have tried renaming and redownloading my certificate from the member center but that didn't work.
A very common "doh!" is you copied over the relevant item in Keychain,
BUT!
you forgot the private key part:
So fi the disclosure triangle on the left is missing and the "key" symbol part is missing, that's what's happened.
Solution: just EXPAND the triangle and highlight BOTH parts, then click export. move the file to your other Mac and open.
ALSO -- don't forget, in Xcode you have to literally login these days.
Xcode - Preferences - second tab == Accounts
It's easy to forget, say, one of your various client's accounts there.
The App Distribution Guide on the Apple Dev site states that this can be a frequent problem if moving from one mac to another (or re-installing in this case). A simple fix would be to export your certificates as a developer profile file from your previous install, but you probably don't have a back up readily available. Try clicking the 'revoke and request' button and see if you can re-download your developer profile file.
Hope this helps, Will