You need to grant permissions to WebWork:

grant {
	permission java.security.AllPermission;
};

or more specifically,

  • Give Write Permissions to java.util.PropertyPermission.
  • Add java.lang.reflect.ReflectPermission "suppressAccessChecks"
  • OgnlInvoke Permission
grant {
	permission java.util.PropertyPermission "*", "read, write";
	permission java.lang.reflect.ReflectPermission "suppressAccessChecks";
	permission ognl.OgnlInvokePermission "*";
};