EDIT:
We have found out that this problem is common to many users starting on February 14th, due to Apple's WWDR Intermediate Certificate expiration.
I have had this problem for the last 6 hours and as much as I have researched it, haven't been able to find the answer.
I updated a previously submitted app, and tried to Archive and Upload it to the app store. However, in the organizer I am getting an error: "Missing iOS Distribution signing identity for [my name]." After a lot of research, I tried reseting my Distribution Certificate in different ways, restarting XCode plus an array of different things.
The closest I got to an answer is that I noticed that my Distribution Certificate in Keychain says "This certificate has an invalid issuer." But I haven't been able to fix that problem either.
Can somebody help?

