The problem you're experiencing is due to a bad datablock on the side of the person hosting the server. This is usually a very hard problem to fix seeing as the person most likely has a lot of add-ons, and also probably doesn't have the time to go in and remove all of them one by one until they find the one that's making you crash. For now, go to another server. If that still doesn't work, re-download and re-install Blockland without keeping your old add-ons.