Passing hashmap as parameter from client to server by rpc

Hi,

I need to pass a hashmap from client to server by rpc. I get the following exception.

unexpected exception: java.lang.UnsatisfiedLinkError: com.google.gwt.user.client.Cookies.loadCookies(Ljava/util/HashMap;)V

I have tried to put the hashmap<String, String> in a serializable class as a wrapper, but I still get the same exception.

Is there any special way to pass the hashmap as input parameters?

Thanks