Minecraft server crashing error help?

This server that I help build now keeps crashing and this is the error it keeps showing:

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A detailed walkthrough of the error, its code path and all known details is as follows:
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-- Head --
Stacktrace:
at net.minecraft.server.v1_7_R1.TileEntity…
at net.minecraft.server.v1_7_R1.TileEntityH…
at net.minecraft.server.v1_7_R1.TileEntityH…
at net.minecraft.server.v1_7_R1.TileEntityH…

-- Block entity being ticked --
Details:
Name: Hopper // net.minecraft.server.v1_7_R1.TileEntityH…
Block type: ID #154 (tile.hopper // net.minecraft.server.v1_7_R1.BlockHopper…
Block data value: 4 / 0x4 / 0b0100
Block location: World: (-181,37,-276), Chunk: (at 11,2,12 in -12,-18; contains blocks -192,0,-288 to -177,255,-273), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Actual block type: ID #154 (tile.hopper // net.minecraft.server.v1_7_R1.BlockHopper…
Actual block data value: 4 / 0x4 / 0b0100
Stacktrace:
at net.minecraft.server.v1_7_R1.World.tickE…
at net.minecraft.server.v1_7_R1.WorldServer…

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