d_pet

I too am having this issue when I start up a minecraft version 1.5.1 server.
I have thumbed the post and will include an excerpt from my server log below.
I am running the current version of java (v7 u17) on a Windows vista computer with SP2 installed.

2013-03-24 13:52:29 [INFO] Preparing start region for level 0
2013-03-24 13:52:30 [SEVERE] Wrong location! ss['arrow'/87, l='SMP_1', x=NaN, y=
NaN, z=NaN]
java.lang.Exception: Stack trace
        at java.lang.Thread.dumpStack(Unknown Source)
        at abw.a(SourceFile:504)
        at acj.a(SourceFile:276)
        at acj.a(SourceFile:72)
        at acj.a(SourceFile:60)
        at iy.f(SourceFile:125)
        at iy.c(SourceFile:76)
        at net.minecraft.server.MinecraftServer.e(SourceFile:224)
        at net.minecraft.server.MinecraftServer.a(SourceFile:194)
        at hz.c(SourceFile:176)
        at net.minecraft.server.MinecraftServer.run(SourceFile:306)
        at gp.run(SourceFile:573)
2013-03-24 13:52:30 [INFO] Preparing spawn area: 48%
2013-03-24 13:52:31 [INFO] Done (2.055s)! For help, type "help" or "?"