Server crash error (I think involving builders)

[D3matt]

Launcher/pack Version: 2.1.1 (Current version)

Operating System: Windows Server 2008 R2

Version of Java: Java 7 Update 3 x64

Description of Problem: I'm not really sure. I check the server in the morning (Or whenever), and the log has the below error followed by a bunch of nothing but groupmanager refreshing and Read Timed Out errors and can't be joined. It seems to work fine upon restarting (until it happens again...)

Error Messages: java.lang.NullPointerException

at net.minecraft.server.World.mayPlace(World.java:2495)

at net.minecraft.server.ItemBlock.a(ItemBlock.java:71)

at buildcraft.builders.TileBuilder.doWork(TileBuilder.java:179)

at buildcraft.api.PowerProvider.update(PowerProvider.java:52)

at buildcraft.core.TileBuildCraft.l_(TileBuildCraft.java:51)

at net.minecraft.server.World.tickEntities(World.java:1182)

at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:534)

at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:441)

at net.minecraft.server.ThreadServerApplication.run(SourceFile:465)

Link to pastebin of log: N/A

EDIT: This crash happened 2 more times since I posted this. Once when I was just fixing griefs in my spawn with nobody else on, and once when 2 other players joined. Possibly caused by a chunk with a builder being loaded and trying to build?

EDIT2: Third time. Definitely caused by loading a certain chink near spawn.

EDIT3: In singleplayer, I found and removed a builder with 29 Reinforced Stone and Template #3 connected through an Energy Link to an HV Solar Array. The crashed stopped after I removed it. It was connected to the Energy Link with (invisible) Item type 166 which crashed my client when I tried to spawn it, throwing this on the server: Error Creating Pipe Type 0 (class=null). I had to delete my player.bat to login again, and now I can't set my game mode, even from the console (But /creative still works).