Here is the crash report: https://gist.github.com/ajthemacboy/9fe6dd219ce9a6c5f646

I have no idea what was 'tested', as the (I can only assume) troll just logged out and is not making contact. I'm sorry I can't be more specific.

Now, when me and the other player login, we immediately crash.

My guess:

-- Entity being ticked --
Details:
    Entity Type: null (net.minecraft.client.entity.EntityClientPlayerMP)
    Entity ID: 297256
    Entity Name: ajthemacboy
    Entity's Exact location: 632.38, 53.52, 335.75
    Entity's Block location: World: (632,53,335), Chunk: (at 8,3,15 in 39,20; contains blocks 624,0,320 to 639,255,335), Region: (1,0; contains chunks 32,0 to 63,31, blocks 512,0,0 to 1023,255,511)
    Entity's Momentum: 0.03, 0.00, 0.06

Somebody forgot to check if a Player was Null before posting that section of Code. Null is usually a bad thing I've noticed lol

Edit: merged posts.

    Server brand: kcauldron,cauldron,craftbukkit,mcpc,fml,forge

Worth noting: KCauldron sometimes causes problems because it'sit changes default values in MineCraft. OptiFine on the other hand is Closed Source (so nobody knows what to not put to avoid breaking it, or what to put to fix the break, except the Author of the Closed Source Code), and thus some Mod Devs don't provide support for it.

Edit: information corrections.

Edit: Merged Posts.
If I'm not mistaken, you've got the wrong Blood Mod for your crash report, that log says BloodArsenal, this is BloodMagic, which that mod is an Add-on to.

Aye, you are using an outdated version of Blood Arsenal, update it to the latest and someone close this

Right team of people at least lol here is the correct issue tracker for you By The Way: _LINK_

Edit: didn't see Arcaratus post just before me lol