Vanilla Server - Players get Disconnected: "Take too long to log in"

Please force a crash by pressing F3 + C for 10 seconds while ingame and attach the crash report here.

UPDATE:

I booted up the server and tried to connect using "localhost" so I could get a good crash report. I now cannot even connect to the server using localhost. There server gave me this error message:

2013-05-17 17:30:41 [INFO] gcman96/127.0.0.1:62397 logged in with entity id 373 at (65.01419573403223, 84.0, 313.11981544714905)
java.lang.NullPointerException
at ek.a(SourceFile:231)
at fh.a(SourceFile:50)
at ek.a(SourceFile:222)
at ck.h(SourceFile:182)
at ck.d(SourceFile:16)
at cm.run(SourceFile:115)
2013-05-17 17:30:41 [INFO] gcman96 lost connection: disconnect.genericReason
2013-05-17 17:30:41 [INFO] gcman96 lost connection: disconnect.genericReason
2013-05-17 17:30:44 [SEVERE] Reached end of stream

It seems I connected and was abruptly disconnected. My client said "End of Stream"

The attached crash report was obtained in an SSP world, so it is unlikely to be of much help. I'll try to connect to my own server again to get a better report.

Also, just glanced at the console to find more error messages:

java.lang.IllegalArgumentException: Empty string not allowed
at cg.<init>(SourceFile:15)
at bu.a(SourceFile:77)
at asc.e(SourceFile:186)
at asc.b(SourceFile:112)
at alj.a(SourceFile:88)
at alj.a(SourceFile:76)
at jb.a(SourceFile:646)
at jb.a(SourceFile:631)
at net.minecraft.server.MinecraftServer.a(SourceFile:265)
at net.minecraft.server.MinecraftServer.r(SourceFile:412)
at net.minecraft.server.MinecraftServer.run(SourceFile:341)
at gr.run(SourceFile:584)

ACTUAL UPDATE:

Much earlier, I deleted a health scoreboard objective to solve the problem of not being able to connect using localhost. Then, I remade the objective. Just now, I tried deleting it again and was able to connect again, so not being able to connect from localhost was probably because of that health objective.

The crash report attached is now from when I was connected to the server.

Server still periodically says

[SEVERE] Reached end of stream

and others are still having trouble connecting

In that case duplicate of MC-15058.

Is the scoreboard the only problem? The real problem is that, even with no scoreboard data, no one can connect except me (using localhost)