Hm, what version of CraftBukkit are you running? And, you might have to reload the server again. There might be a very rare bug in ProtocolLib that causes it, but I have been unable to reproduce it properly. When it does occur (rarely), I'm never able to debug it, as recompiling or reloading the server fixes it. In any event, I've updated BlockAPI. Had to fix some serious client crashes that were caused by the byte value overflowing into negative numbers (whoever decided to make byte signed should be shot). I've also renamed it to BlockPatcher, just like you suggested, and moved the testing code out into a separate plugin (BlockTest). That way, it won't conflict with future users of the API. You can get BlockPatcher here. In addition, I've noticed a pretty serious bug with ProtocolLib. If you're running 1.3.2, you're guaranteed to fall into the void when you log on the server. So, I guess I have to release yet another version today. You can get it here.