This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Generally java.util.ConcurrentModificationException will occur when one thread to modify a Collection while another thread is iterating over it. Please check your code with this viewpoint. Below approach can be considered.
 Copy the collection object to be modified
 Modify the collection object inside the synchronized block