Placing a crane backpack on an armor stand crashes the player and every client in the range of the block, and they will be unable to log back in.

Crash log: http://pastebin.com/bDpJAYF6

A lot of people seem to be doing it as well: https://www.google.com/search?q=openblocks+crane+backpack+armor+stand&qscrl=1

I fixed it, although looks like it was improper usage on Bibliocraft side (already fixed in recent versions)