I was on my private server, then I used /jump to go somewhere else fast, then the server crashed.
http://pastebin.com/5H0snjXN
(For some reason, format ending (ex. /spoiler) refuses to work anymore. So, I pastebin'd the crashlogs.)
Mod List:
Archimede's Ships
Artifice (v 1.1.3-243)
Backpacks (v 1.26.29)
Better Storage (v 0.8.0.45)
Bibliocraft (v 1.4.0)
Biomes O' Plenty (v 1.2.1.416)
Carpenter's Blocks (v 2.0.4)
Chisel (v 1.5.0 fix)
Ex Nihilo (v 1.28)
Ex Aliquo (v 0.9.2)
Enhanced Portals 2 (v1.0.9)
Extended Renderer
Food Plus (v2.7-PRE)
Forge Multipart (v 1.0.0.106)
Inventory Tweaks (v 1.56-b77)
Iron Chest (v 5.3.14.512)
Minefactory Reloaded (v 2.7.5-352)
Mystcraft (v 0.10.12.1)
MCPC (v 1.6.4 R2.1)
Natura (v 2.1.14)
Necromancy
Not Enough Items (v 1.6.1.9)
Not Enough Keys (v 0.0.4)
Noppe's Custom NPC Mod (v 1.6.2/1.6.4)
OpenBlocks (v 1.2.5)
Project Red [Base, Compat, Integration, Lighting, Mechanical, World] (v4.3.2.26)
qCraft (v 1.1)
Secret Rooms (v 4.6.2.323)
Statues (v 2.1.1)
Tinker's Construct (v 1.5.4d4)
Tinker's Mechworks (v 0.1.4.2)
Thaumcraft (v 4.1.0)
Thaumic Tinkerer (v 2.3-137)
Thermal Expansion (v 3.0.0.2)
Waila (v 1.5.1)
Witchery (v 0-15-1 164)
EDIT: Hm, I removed Biomes O' Plenty thinking that was the issue, and it worked for a while, but recently a player on my server crashed it, and i received a very similar error: http://pastebin.com/bkL5a2yn
EDIT 2: So, what we know so far is its a spawning structure from an unknown mod, and that I was unable to find a crashing chunk in singleplayer. We have gone through our client and server modlists, they are identical.
A different crashlog after messing with forgechunkloader config: http://pastebin.com/fwRgwdxc
EDIT 3: Okay, maybe it's not caused by a chunk, I logged in an area that we knew was safe of this, we had adventured quite a distance in a circle around it, but upon logging in, server crashed. http://pastebin.com/zVLRWxni
EDIT 4: So every time two people are on the server, it crashes. But it's weird, people can still chat for about 20-30 seconds and read it, despite console stating a crashlog was made. (though, after that 20-30s, it fully crashes.)
None of us have a clue on how to fix this or what the crashlog means. (Us is myself, server staff, and current whitelisted players. We already have a few on for playtesting. They're what found this.)
http://pastebin.com/5H0snjXN
(For some reason, format ending (ex. /spoiler) refuses to work anymore. So, I pastebin'd the crashlogs.)
Mod List:
Artifice (v 1.1.3-243)
Backpacks (v 1.26.29)
Better Storage (v 0.8.0.45)
Bibliocraft (v 1.4.0)
Biomes O' Plenty (v 1.2.1.416)
Carpenter's Blocks (v 2.0.4)
Chisel (v 1.5.0 fix)
Ex Nihilo (v 1.28)
Ex Aliquo (v 0.9.2)
Enhanced Portals 2 (v1.0.9)
Extended Renderer
Food Plus (v2.7-PRE)
Forge Multipart (v 1.0.0.106)
Inventory Tweaks (v 1.56-b77)
Iron Chest (v 5.3.14.512)
Minefactory Reloaded (v 2.7.5-352)
Mystcraft (v 0.10.12.1)
MCPC (v 1.6.4 R2.1)
Natura (v 2.1.14)
Necromancy
Not Enough Items (v 1.6.1.9)
Not Enough Keys (v 0.0.4)
Noppe's Custom NPC Mod (v 1.6.2/1.6.4)
OpenBlocks (v 1.2.5)
Project Red [Base, Compat, Integration, Lighting, Mechanical, World] (v4.3.2.26)
qCraft (v 1.1)
Secret Rooms (v 4.6.2.323)
Statues (v 2.1.1)
Tinker's Construct (v 1.5.4d4)
Tinker's Mechworks (v 0.1.4.2)
Thaumcraft (v 4.1.0)
Thaumic Tinkerer (v 2.3-137)
Thermal Expansion (v 3.0.0.2)
Waila (v 1.5.1)
Witchery (v 0-15-1 164)
EDIT: Hm, I removed Biomes O' Plenty thinking that was the issue, and it worked for a while, but recently a player on my server crashed it, and i received a very similar error:
http://pastebin.com/bkL5a2yn
EDIT 2: So, what we know so far is its a spawning structure from an unknown mod, and that I was unable to find a crashing chunk in singleplayer. We have gone through our client and server modlists, they are identical.
A different crashlog after messing with forgechunkloader config: http://pastebin.com/fwRgwdxc
EDIT 3: Okay, maybe it's not caused by a chunk, I logged in an area that we knew was safe of this, we had adventured quite a distance in a circle around it, but upon logging in, server crashed. http://pastebin.com/zVLRWxni
EDIT 4: So every time two people are on the server, it crashes. But it's weird, people can still chat for about 20-30 seconds and read it, despite console stating a crashlog was made. (though, after that 20-30s, it fully crashes.)
I would, except for the part that it feels like this is caused by a mod. I've hosted multiple private servers never having this issue.