I am trying to open Attack of the B-Team as soon as the downloading ends launcher closes and pops up again and nothing happens. I have the same problem with the Normal Tekkit and I think some modpacks too. I have reinstalled it for couple of times, changed the RAM that it uses, changed the version and changed it to beta too but nothing helped.
EDIT: I didn't know that there was a special place for these issues but I couldn't delete the post so, sorry