Old world doesn't work with 1.4

Alright, so I have been running a 1.3.2 server for a while using bukkit's recommended build. Now the 1.4 update came out, and I got the official 1.4 minecraft.jar and put it in a new folder along with a new run.bat.

Then i copied the world from my old server files into the new one. Thats when the problem started. For some reason, every single time anyone who hadnt been on before tried to connect, they would get a crash message. Then after a short while, it started happening to the people who HAD logged in before.

Code:
---- Minecraft Crash Report ----
// Quite honestly, I wouldn't worry myself about that.

Time: 10/25/12 4:27 PM
Description: Unexpected error

java.lang.ArrayIndexOutOfBoundsException
at java.lang.System.arraycopy(Native Method)
at za.a(SourceFile:818)
at awr.a(SourceFile:864)
at dl.a(SourceFile:135)
at bx.b(SourceFile:341)
at awr.d(SourceFile:98)
at awu.c(SourceFile:69)
at net.minecraft.client.Minecraft.l(SourceFile:1080)
at net.minecraft.client.Minecraft.J(SourceFile:582)
at net.minecraft.client.Minecraft.run(SourceFile:534)
at java.lang.Thread.run(Unknown Source)

Relevant Details:
- Minecraft Version: 1.4.2
- Operating System: Windows 7 (amd64) version 6.1
- Java Version: 1.7.0_07, Oracle Corporation
- Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
- Memory: 445841456 bytes (425 MB) / 514523136 bytes (490 MB) up to 954466304 bytes (910 MB)
- JVM Flags: 2 total; -Xms512m -Xmx1024m
- AABB Pool Size: 10817 (605752 bytes; 0 MB) allocated, 10817 (605752 bytes; 0 MB) used
- LWJGL: 2.4.2
- OpenGL: AMD Radeon HD 7770 GL version 4.2.11411 Compatibility Profile Context, ATI Technologies Inc.
- Is Modded: Very likely
- Type: Client
- Texture Pack: Default
- Profiler Position: N/A (disabled)
- Vec3 Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
- World MpServer Entities: 16 total; [axc['thirdfangs'/3612, l='MpServer', x=232.50, y=89.24, z=-315.50], og['Bat'/3637, l='MpServer', x=209.50, y=21.00, z=-299.50], og['Bat'/3636, l='MpServer', x=208.50, y=21.00, z=-300.50], qa['Zombie'/3616, l='MpServer', x=251.50, y=17.00, z=-295.50], qa['Zombie'/3615, l='MpServer', x=252.50, y=17.00, z=-294.50], pw['Skeleton'/3614, l='MpServer', x=251.50, y=62.00, z=-314.50], ayn['XxNeon_ColorsxX'/2440, l='MpServer', x=249.50, y=86.25, z=-315.50], pw['Skeleton'/70, l='MpServer', x=208.38, y=20.00, z=-303.72], pw['Skeleton'/73, l='MpServer', x=216.88, y=63.00, z=-300.56], pw['Skeleton'/2797, l='MpServer', x=209.50, y=20.00, z=-302.50], pl['Creeper'/93, l='MpServer', x=233.50, y=41.00, z=-297.50], pl['Creeper'/92, l='MpServer', x=236.50, y=30.00, z=-290.50], qa['Zombie'/89, l='MpServer', x=229.50, y=13.00, z=-291.50], pl['Creeper'/2344, l='MpServer', x=251.72, y=61.00, z=-312.75], py['Spider'/3707, l='MpServer', x=198.50, y=29.00, z=-312.50], py['Spider'/3738, l='MpServer', x=221.50, y=17.00, z=-281.50]]
- World MpServer Players: 2 total; [axc['thirdfangs'/3612, l='MpServer', x=232.50, y=89.24, z=-315.50], ayn['XxNeon_ColorsxX'/2440, l='MpServer', x=249.50, y=86.25, z=-315.50]]
- World MpServer Chunk Stats: MultiplayerChunkCache: 45
- Forced Entities: 17 total; [py['Spider'/3707, l='MpServer', x=198.50, y=29.00, z=-312.50], axc['thirdfangs'/3612, l='MpServer', x=232.50, y=89.24, z=-315.50], qa['Zombie'/3615, l='MpServer', x=252.50, y=17.00, z=-294.50], pw['Skeleton'/70, l='MpServer', x=208.38, y=20.00, z=-303.72], pw['Skeleton'/3614, l='MpServer', x=251.50, y=62.00, z=-314.50], ayn['XxNeon_ColorsxX'/2440, l='MpServer', x=249.50, y=86.25, z=-315.50], ayn['XxNeon_ColorsxX'/2440, l='MpServer', x=249.50, y=86.25, z=-315.50], pl['Creeper'/2344, l='MpServer', x=251.72, y=61.00, z=-312.75], og['Bat'/3637, l='MpServer', x=209.50, y=21.00, z=-299.50], og['Bat'/3636, l='MpServer', x=208.50, y=21.00, z=-300.50], pw['Skeleton'/73, l='MpServer', x=216.88, y=63.00, z=-300.56], py['Spider'/3738, l='MpServer', x=221.50, y=17.00, z=-281.50], pw['Skeleton'/2797, l='MpServer', x=209.50, y=20.00, z=-302.50], pl['Creeper'/93, l='MpServer', x=233.50, y=41.00, z=-297.50], pl['Creeper'/92, l='MpServer', x=236.50, y=30.00, z=-290.50], qa['Zombie'/89, l='MpServer', x=229.50, y=13.00, z=-291.50], qa['Zombie'/3616, l='MpServer', x=251.50, y=17.00, z=-295.50]]
- Retry Entities: 0 total; []
I dont belive that the modding had anything to do with it as it was happening to somewhere around 20 or 30 different people who tried to log in.
I know it says client error, but only ahppening on this particular server? im at a loss.

I rmoved the copied world files and let minecraft generate their own so my server is running fine now, I would just like to have the world everyone worked so hard on back up and running.

If you want to discuss it more with me in a more direct fashion, ill be on my server most of today its
vipers.kicks-ass.net

You guys are my only hope...