What happened: Server crashed after placing dragon heads in a stack
Steps to produce: 1. Place down a clay block. 2. Place a dragon skull on that block. 3. break clay block. 4. Place dragon head underneath first one.
My server crashed giving me the attached message. Now I cannot load up that world. Server is still running, but cannot log in. I tried a server restart, but still cannot log in.
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UPDATE
Dragon heads had no effect. It was the placing of a sign. As soon as a sign was placed, the server crashed and allows no one back in.