those error messages are useless, especially when they imply it is a temporary problem with app engine, when most likely it is a problem with your certificate.
I have seen this same error message previously if you try to upload a 4096 bit certificate - App engine can only cope with 2048 max.
I had this same problem last week when I tried to reupload a certicate and private keys. I used an old file and the private keys didn't match the certicate.
App engine gave me that same generic error message, it wasn't untill I checked the files I was trying to upload on this site, I realized it was a problem with my ceritficate and not app engine.
some parts of the appengine ecosystem are really half-baked...