Minecraft crashes with the attached error when attempting to place a minecart on a powered rail. I tested on both older worlds created over 6 months (SSP) ago and on a newly created world (CSP). The crash occurred for both the powered and unpowered state of the powered rail. There was always a block of stone next to the powered rail. On attempting to reload the world after the crash minecraft would attempt to load the world and begin rendering and then crash after several moments.