What's the item you're trying to pick up
Does this happen on any server, or only yours?If it is on yours, do other player have the same problem?Does it also happen if you change your players datablock?
To fix this, I think the fastest and easiest way will be to reinstall Blockland.The standard playertype is not just an addon, it is hardcoded into the game.Don't forget to backup your addons & saves