Hmm, i looked and, the first i think, 1. The server may not have enough memory as it is overloaded. Or 2. You get an invalid item, ok i dont know what item you pick, if the kick happend whit all items not its this, but its happend only whit one item, dont pickaxe this item, ok?
It happens with all items. Also, I can't think why the server would possibly be overloaded, as we're not doing all that much on it. Thank you for the help, though.