The FTB Forum is now read-only, and is here as an archive.
To participate in our community discussions, please join our Discord! https://ftb.team/discord
Just a thought so please do not hate me for saying this. You need a premium minecraft account to log in at least once to download the packs and install the mods and minecraft. If you transferred this folder from another computer that you own then it might be the launcher's encryption to ensure that you are a premium user. Try logging in again.
I ask this because of these entries:
"[ERROR] ErrorUtils.tossError:26: Login failed: User not premium"
"[10:38:45] [ERROR] ClassLoader.checkCerts:-1->MinecraftLauncher.main:214: Unhandled error launching minecraft: java.lang.SecurityException: class "sq"'s signer information does not match signer information of other classes in the same package"
Yup, "not premium" means a cracked version of the game.
FTB does not play with thieves. Dinnerbone might not care if you don't pay for his work, but it would be wrong of FTB to encourage theft of somebody else's work.
I sometimes get the same error, but only on one specific mod pack, new world mod pack, and I have a premium account. anyway, I cannot get new world mod pack to start.