same here since yesterday.
http://pastebin.com/3KkZs1PJ
I tried to cancel the ftb installation folder and re-install the launcher but it worked only the first time. also tried install both the .exe and the .jar file but nothing changed.
I have installed the Direwolf20, the Ultimate and the RPG modpacks and I can download and play all of them without problems only on the first run.
When I close the app and reopen, then it appears the one I called "the gray console of death".
Before throwing my pc from the window, I gave a chance to MultiMC (I feel kinda uncomfortable saying this) just to say "I've tried everything". I've imported the packs from ftb and they worked fine, so I assume it's a launcher related problem.
I forgot to say that now every time I try to run the ftb launcher, the console runs the java process in background, as i could see from task manager, and not like an "open app" like it usually do when it works fine.
then every time i reopen the launcher, it appear another java process in background. so closing the console doesn't kill the process, I have to kill it manually. I hope i have explained it properly.
Sorry for bad English
and thanks in advance for replies.
