I had success. and posted in another thread.

ops Posted at 2016-4-7 18:22
My P3 Pro has been able to upgrade, but the RC hasn't upgraded.
Now I am in the same situation as  ...

I Have same problem I try to many way to upgrade RC but til not working, someone can help if can let me know how to upgrade RC thanks so much

ruvanbui Posted at 2016-6-4 11:57
I Have same problem I try to many way to upgrade RC but til not working, someone can help if can l ...

You can try another proxy, for example http://advanced.name/  and you could upgrade again. It helped me somehow