Is it a mod, or another way to remove blocks without logging in to the server? I have a server but someone has placed a world anchor thats crashing the server when we try to log on.
Sorry for necroing this but as it's the first result when googling after console removal of items and there is a far easier solution:
Go to the servers console and execute the following command: /execute @e ~ ~ ~ setblock x y z air
You can normally find the x y z coordinates of the block crashing the client in the crashlog of minecraft. In case there is no entity found to execute the command on login and execute it on the console between loging in and crashing.
You have a few options here. The following is a list of things that you can do, starting from easiest/most convenient to harder/less convenient.
The most convenient thing to do would be to delete the world and to start over. Of course, this is the easiest thing to do, meaning that it is also associated with dire consequences. If you have anything worth keeping, you may want to port it over using WorldEdit/MCEdit. If you find that too complicated, do not use this solution.
If you open the world in vanilla, and then save it and put it back on the server, this may also fix the problem. This may also remove your non-vanilla placed blocks. You probably would not want this if you have large things that you do not want to lose.
Another solution is to delete the mod and the configuration file(s)/folder(s) that has the world anchor. Then run the game normally, save, and put the mod back on.
The most complex solution is to find the item ID of the world anchor and to use WorldEdit to remove it. However, this requires you to log into the server, which you cannot do. If the server does not immediately crash, you may have enough time to type the command, assuming you are close to it. Assuming the anchor has Item ID 483, you would do
//replacenear 100 483 0, where 100 is the radius (relevant to where you are currently standing, 483 the item ID, and 0 as the item ID of the item you want to change it to.