Placing sign kicks players

I placed a sign and the second I placed it I was kicked from the server. Every time I or another player tries to join, they are kicked, given the kick message attached to this report. The server has also crashed twice, giving the following log:

---- Minecraft Crash Report ----
// Oh - I know what I did wrong!

Time: 7/29/15 9:55 PM
Description: Exception ticking world

java.lang.OutOfMemoryError: Java heap space
	at java.util.Arrays.copyOfRange(Unknown Source)
	at java.lang.String.<init>(Unknown Source)
	at java.lang.StringBuffer.toString(Unknown Source)
	at java.io.StringWriter.toString(Unknown Source)
	at com.google.gson.Gson.toJson(Gson.java:528)
	at com.google.gson.Gson.toJson(Gson.java:507)
	at eu$a.a(SourceFile:195)
	at amx.b(SourceFile:34)
	at aov.a(SourceFile:236)
	at aov.a(SourceFile:95)
	at lf.b(SourceFile:156)
	at lf.d(SourceFile:228)
	at lg.d(SourceFile:185)
	at net.minecraft.server.MinecraftServer.B(SourceFile:599)
	at kp.B(SourceFile:299)
	at net.minecraft.server.MinecraftServer.A(SourceFile:535)
	at net.minecraft.server.MinecraftServer.run(SourceFile:451)
	at java.lang.Thread.run(Unknown Source)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
	at java.util.Arrays.copyOfRange(Unknown Source)
	at java.lang.String.<init>(Unknown Source)
	at java.lang.StringBuffer.toString(Unknown Source)
	at java.io.StringWriter.toString(Unknown Source)
	at com.google.gson.Gson.toJson(Gson.java:528)
	at com.google.gson.Gson.toJson(Gson.java:507)
	at eu$a.a(SourceFile:195)
	at amx.b(SourceFile:34)
	at aov.a(SourceFile:236)
	at aov.a(SourceFile:95)
	at lf.b(SourceFile:156)
	at lf.d(SourceFile:228)
	at lg.d(SourceFile:185)

-- Affected level --
Details:
	Level name: world
	All players: 0 total; []
	Chunk stats: ServerChunkCache: 559 Drop: 255
	Level seed: -1148845891
	Level generator: ID 00 - default, ver 1. Features enabled: true
	Level generator options: 
	Level spawn location: -248.00,64.00,244.00 - World: (-248,64,244), Chunk: (at 8,4,4 in -16,15; contains blocks -256,0,240 to -241,255,255), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Level time: 445677 game time, 448555 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 113800 (now: false), thunder time: 25126 (now: false)
	Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
Stacktrace:
	at net.minecraft.server.MinecraftServer.B(SourceFile:599)
	at kp.B(SourceFile:299)
	at net.minecraft.server.MinecraftServer.A(SourceFile:535)
	at net.minecraft.server.MinecraftServer.run(SourceFile:451)
	at java.lang.Thread.run(Unknown Source)

-- System Details --
Details:
	Minecraft Version: 15w31a
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_55, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 539382848 bytes (514 MB) / 2025324544 bytes (1931 MB) up to 2025324544 bytes (1931 MB)
	JVM Flags: 0 total; 
	IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
	Profiler Position: N/A (disabled)
	Player Count: 0 / 8; []
	Is Modded: Unknown (can't tell)
	Type: Dedicated Server (map_server.txt)