It first started out when I tried building a Reinforced Iron Chest, part of Improved Storage. After attempting to open the chest (to compare its storage capacity against that of a regular chest) the game closed completely to the launcher. The game now crashes completely when trying to re-enter.
(standing nearby / same chunk as the chest, but it did not crash when first placing the chest, and now it crashes immediately when the world loads?)
[All previous messages seem pretty much the same an not much use at all, they are just a list of the name of every mod in the pack.]