XStream Clases Used in Applet Throwing Security Exceptions

Here i am placing my exception. I signed that jar. Please tell me how to overcome this Exception without changing the java policy file.
java.security.AccessControlException: access denied (java.lang.RuntimePermission createClassLoader)
at java.security.AccessControlContext.checkPermission(Unknown Source)
at java.security.AccessController.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkCreateClassLoader(Unknown Source)
at java.lang.ClassLoader.<init>(Unknown Source)
at com.thoughtworks.xstream.core.util.CompositeClassLoader.<init>(CompositeClassLoader.java:39)
at com.thoughtworks.xstream.XStream.<init>(XStream.java:191)
at com.thoughtworks.xstream.XStream.<init>(XStream.java:181)
at com.thoughtworks.xstream.XStream.<init>(XStream.java:169)
at com.sdt.utp.business.globalcache.navigatorviews.ObjectInvokeActionHandler.convertXMLTOObject(Unknown Source)
at com.sdt.utp.business.globalcache.navigatorviews.ObjectInvokeActionHandler.getObjectFromURL(Unknown Source)
at com.sdt.utp.business.globalcache.navigatorviews.ObjectInvokeActionHandler.handle(Unknown Source)
at com.sdt.utp.client.Navigator.RefreshAdministrationTree(Unknown Source)
at com.sdt.utp.client.Navigator.refresh(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.plugin.javascript.invoke.JSInvoke.invoke(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.plugin.javascript.JSClassLoader.invoke(Unknown Source)
at sun.plugin.com.MethodDispatcher.invoke(Unknown Source)
at sun.plugin.com.DispatchImpl.invokeImpl(Unknown Source)
at sun.plugin.com.DispatchImpl$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.plugin.com.DispatchImpl.invoke(Unknown Source)
java.lang.Exception: java.security.AccessControlException: access denied (java.lang.RuntimePermission createClassLoader)
at sun.plugin.com.DispatchImpl.invokeImpl(Unknown Source)
at sun.plugin.com.DispatchImpl$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.plugin.com.DispatchImpl.invoke(Unknown Source)