I'm trying to fix this problem, but in any case I do does not fix. Could someone help me?
for(Iterator<Block> iterator = event.blockList().iterator(); iterator.hasNext();)
{
Block b = iterator.next();
if (((RegiaoCuboid) r).contains(b))
event.blockList().remove(b);
}
Remove using the iterator:
iterator.remove();
A ConcurrentModificationException is thrown when a collection changes in a manner which invalidates open iterators. In this case you are calling remove directly on the collection.
You can't modify a List while iterating over it. I would suggest adding the Blocks you wish to remove to a new List, then iterating over that and removing them from the main one (EDIT: Or, do what the other person said). Additionally, if you're doing what I think you are, I would suggest asking further questions on the Bukkit Forums. This question is more general, but Bukkit-specific questions will be more easily answered by individuals who are familiar with the area.
Iterator has a remove method.