I'm having the same issue, but heres what I've found;
When this issue occurs, its random. I dont know what causes it, but I think it has something to do with changing your skin? Its happened twice when I've changed my skin. But if I leave it for a day, and come back, boom! It's up and running, I dont think it has anything to do with minecraft.net or mojang, or even B-team. I think its just a glitch, but I cant be sure. Im actually having this issue right now. Here are some things that might work.
*Log out of the technic launcher, and log back in.
*Wait 24 hours, and try again.
*Click the cog icon below the pack you want to launch, and then click 'reset modpack'.
*Make sure you have enough GB's put into your game, you may get the message because the server is overloading you.
Any suggestions to add to this list?
I hope this helps some, for me, waiting or logging in again fixes it.