Forge 1231
Mariculture-Deluxe-1.7.10-161

http://pastebin.com/mDcpNH8m

Here is the conversation I had with the player on my server who was having this problem:
"BBoldt: can you tell me what you were doing exactly? I can't seem to reproduce this
BBoldt: what were you trying to convert
BBoldt: and how were you inserting it?
Player: first when I wanted to convert mekanism seel to tinker's, just selected the version and put an ingot in the slot
Player: then i tried with some lapis blocks, I put the whole stack, still crashed
BBoldt: must be a multiplayer thing
BBoldt: I'll submit a bug report, use a unifier for now"