[WARNING] Player Moved too quickly! Help!

So I run a fairly popular server that's been up for a few months now, and we have just gotten an interesting problem that I can't seem to solve! Out of nowhere, a lot of my playerbase has been getting an error upon trying to login to the server. Here is what I see in console:

[INFO] PlayerName [IP Address] logged in with entity id 12345 at ([world] 1564.6176761071772, 78.0, 5819.562635548683)
[WARNING] PlayerName Moved too quickly!


Now, in the game, it shows them as logging in and then logging right offline. The message above is all it shows, doesn't show a "disconnecting" message or anything in the console. It also doesn't happen to everyone, it's maybe a dozen or so different players so far. Some of them get the error constantly, and can't login, some can try over and over and eventually they'll be able to get in.

The only solution I have come up with, is deleting the users .dat file. It then logs them in at spawn, and they can log right in. So is there perhaps some error where they are logging out that's causing them to get this error? I havn't done any plugin updates or anything recently, and it just started happening randomly a day ago.


Here's our system specs:
- Intel Xeon E3-1230 3.2 Ghz
- 16Gb RAM
- 60Gb SSD and 1 TB HDD (Servers on the SSD)
- Runs on CentOs 5 64bit

Plugin List:
AlphaChest
Quicksign
SignRank
AutoDisc
GroupManager
WorldEdit
FlatlandsBuilder
SpleefUltimate
Vault
Stargate
Multiverse-Core
WorldGuard
AutoMessage
MineBackup
SimplyVanish
CasinoSlots
EndReset
SignThatBlock
DisguiseCraft
LotteryPlus
BASpleef
CoreProtect
MobSpawnControl
TimeLock
BKCommonLib
Votifier
MobArena
mcMMO
FoundDiamonds
Essentials
hatMe
MagicCarpet
ATMsigns
MobDisguisePVPControl
EssentialsSpawn
Multiverse-Portals
Multiverse-Inventories
Multiverse-NetherPortals
SignShop
LWC
dynmap
EssentialsChat
WorldBorder
AlphaChest
QuickSign
WhitelistCommand


Also, our current world is QUITE large. It's a 10k by 10k and sitting around 2.2Gb compressed. So if it's something I need to fix with the world file, please give me some solutions, as I am stuck as how to fix this. Any help would be fantastic! Thanks!

 

PHP:

allow-flight=true

 

go to bukkit.yml and find kick on speed hack or something and set it to false