Remove blocks without logging in to the minecraft server

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.

You can use MCEdit to load the map and delete the block, however all the non-vanilla blocks will be invisible, so you'll have to know where it is before loading MCEdit. But you can view the block ID so you can check it's the right block before deleting it.

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.