Crash report: http://pastebin.com/i16FfR2W

Don't know what else to say. I'm the creator of the modpack. The server is Cauldron, but we tested the modpack a lot (including biplanes from YeOlde content pack) on a Cauldron server before we released it and it never crashed.

Well, it doesn't seem to be happening now. Closing this issue, if it happens again I will re-do this!