I searched and I looked at the last few days of posts and didn't see anything related, so here it goes.
Recently I updated my mod pack from build 933 to 946, and I started getting these errors. I upgraded to 949 tonight to see if it solved the issue (it doesn't). The crash happens whenever you look at blocks that apply use the fakeplayer code (it's happened so far to Bibliocraft Armor stands (example in the log) and Tinkerer's Construct Drawbridges, which makes me think it may be a Forge issue). So far the crash has happened to both myself and one of my players. Anyways, for the logs and crash-reports:
Log:
https://gist.github.com/LezCraft/7446237
Crash-Report:
https://gist.github.com/LezCraft/7446266