Switching Worlds 1.6 - 1.7

So Bascily I Am Making A Map In 1.6 Cause I Need Bukkit And I Switched over to 1.7 but when i join i get this error:

[16:42:14] [Server thread/INFO]: Spikey56 joined the game
[16:42:18] [Server thread/WARN]: Failed to handle packet for /127.0.0.1:55914
java.lang.IllegalArgumentException: n must be positive
        at java.util.Random.nextInt(Unknown Source) ~[?:1.7.0_21]
        at agm.a(SourceFile:130) ~[1.7_Minecraft_Server.jar:?]
        at agm.a(SourceFile:27) ~[1.7_Minecraft_Server.jar:?]
        at agg.a(SourceFile:362) ~[1.7_Minecraft_Server.jar:?]
        at ago.a(SourceFile:29) ~[1.7_Minecraft_Server.jar:?]
        at apl.a(SourceFile:432) ~[1.7_Minecraft_Server.jar:?]
        at mi.a(SourceFile:160) ~[1.7_Minecraft_Server.jar:?]
        at aoj.a(SourceFile:781) ~[1.7_Minecraft_Server.jar:?]
        at mi.c(SourceFile:95) ~[1.7_Minecraft_Server.jar:?]
        at mh.<init>(SourceFile:31) ~[1.7_Minecraft_Server.jar:?]
        at mg.a(SourceFile:212) ~[1.7_Minecraft_Server.jar:?]
        at mg.a(SourceFile:249) ~[1.7_Minecraft_Server.jar:?]
        at ld.a(SourceFile:155) ~[1.7_Minecraft_Server.jar:?]
        at ld.c(SourceFile:206) ~[1.7_Minecraft_Server.jar:?]
        at ld.a(SourceFile:100) ~[1.7_Minecraft_Server.jar:?]
        at nd.c(SourceFile:87) ~[1.7_Minecraft_Server.jar:?]
        at nd.a(SourceFile:52) ~[1.7_Minecraft_Server.jar:?]
        at ef.a(SourceFile:166) ~[1.7_Minecraft_Server.jar:?]
        at ms.c(SourceFile:134) [1.7_Minecraft_Server.jar:?]
        at net.minecraft.server.MinecraftServer.u(SourceFile:529) [1.7_Minecraft
_Server.jar:?]
        at lj.u(SourceFile:265) [1.7_Minecraft_Server.jar:?]
        at net.minecraft.server.MinecraftServer.t(SourceFile:441) [1.7_Minecraft
_Server.jar:?]
        at net.minecraft.server.MinecraftServer.run(SourceFile:358) [1.7_Minecra
ft_Server.jar:?]
        at ky.run(SourceFile:617) [1.7_Minecraft_Server.jar:?]
[16:42:18] [Server thread/WARN]: Can't keep up! Did the system time change, or i
s the server overloaded? Running 3868ms behind, skipping 77 tick(s)
[16:42:18] [Server thread/ERROR]: Encountered an unexpected exception
s: Exception getting block type in world
        at net.minecraft.server.MinecraftServer.u(SourceFile:507) ~[1.7_Minecraf
t_Server.jar:?]
        at lj.u(SourceFile:265) ~[1.7_Minecraft_Server.jar:?]
        at net.minecraft.server.MinecraftServer.t(SourceFile:441) ~[1.7_Minecraf
t_Server.jar:?]
        at net.minecraft.server.MinecraftServer.run(SourceFile:358) [1.7_Minecra
ft_Server.jar:?]
        at ky.run(SourceFile:617) [1.7_Minecraft_Server.jar:?]
Caused by: java.lang.RuntimeException: Already decorating!!
        at agm.a(SourceFile:21) ~[1.7_Minecraft_Server.jar:?]
        at agg.a(SourceFile:362) ~[1.7_Minecraft_Server.jar:?]
        at ago.a(SourceFile:29) ~[1.7_Minecraft_Server.jar:?]
        at apl.a(SourceFile:432) ~[1.7_Minecraft_Server.jar:?]
        at mi.a(SourceFile:160) ~[1.7_Minecraft_Server.jar:?]
        at aoj.a(SourceFile:775) ~[1.7_Minecraft_Server.jar:?]
        at mi.c(SourceFile:95) ~[1.7_Minecraft_Server.jar:?]
        at mi.d(SourceFile:108) ~[1.7_Minecraft_Server.jar:?]
        at afn.e(SourceFile:311) ~[1.7_Minecraft_Server.jar:?]
        at afn.a(SourceFile:249) ~[1.7_Minecraft_Server.jar:?]
        at afn.a(SourceFile:1720) ~[1.7_Minecraft_Server.jar:?]
        at aga.a(SourceFile:153) ~[1.7_Minecraft_Server.jar:?]
        at aga.a(SourceFile:101) ~[1.7_Minecraft_Server.jar:?]
        at mj.b(SourceFile:117) ~[1.7_Minecraft_Server.jar:?]
        at net.minecraft.server.MinecraftServer.u(SourceFile:503) ~[1.7_Minecraf
t_Server.jar:?]
        ... 4 more
[16:42:18] [Server thread/ERROR]: This crash report has been saved to: C:\Users\
TheAussieAusten\Desktop\Everything\Minecraft\Servers\Minecraft 1.7 Server\.\cras
h-reports\crash-2013-11-14_16.42.18-server.txt

I thought it was that roses are on the map and 1.7 removed roses so I removed them and that didn't work! I tried another world and it worked perfectly.

Help
~ Austen