1. Try using Granite Pickaxe made of Red or Black Granite Rocks.
2. That is a Forge Bug and it happens in all Modpacks. It annoys the shit out of me too. If you launch a World and get thrown back to the Title Screen instead and then try again then get thrown back again and then try again and launch the world successfully then you have to kill the process afterwards.
1. But Granite is too hard to be mined with a weaker material, isn't it? How do I get a material strong enough excluding default stone, because that feels like cheating(Since the guide says "Stone if you have absolutely nothing else").
2. Are you sure? The same 1.7.10 version that I use for GT, I also use for other mods and packs, but while it consistently happens in GT, I do not recall it happening on the others.