I tried all the usual steps, different browser etc. but in the end I resorted to raising a TAC case. Here's what we found:
404 error is a "not found" error, so we could rule out certificates. DNS name was resolving fine, so the problem was diagnosed to the Social Miner server. With remote access and root privileges, TAC determined that required packages just weren't there!
There was either something wrong with the upgrade file (MD5 was fine though) or most likely it was down to the fact that I did the upgrade, then applied the ES, then the language pack update. TAC advised that the lang pack should have been applied before the ES (In the order they were released).
To solve the issue, the SM server was rolled back to the previous version, then upgraded again.
I hope this help others!
