To enable advanced encryption (such as AES 256), locate the "local_policy.jar" file in your {java_home}/lib/security directory, rename it and replace it by the "local_policy.jar" which is contained in the {areca_home}/lib directory.

For more informations, have a look at the "Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files" topic on Sun's website (java.sun.com)