Just thought I'd post this to help anyone else coping with this error message.

expected end of call ('z') at 'M'. Check method arguments and ensure method overloading is enabled if necessary

Here is the fix:

package uk.co.bigsoft.app.hessian.clients;

import java.net.MalformedURLException;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.caucho.hessian.client.HessianProxyFactory;

public class HessianInterfaceFactory {

    private static final Logger L = LoggerFactory.getLogger(HessianInterfaceFactory.class);

    private HessianProxyFactory factory = new HessianProxyFactory();

    public HessianInterfaceFactory() {
        factory = new HessianProxyFactory();
        factory.setOverloadEnabled(true);
    }

    public T createHessianInterface(Class T type, String url) {

        try {
            return type.cast(factory.create(type, url));
        } catch (MalformedURLException e) {
            L.error("Creating proxy for \"" + type.toString() + "\" on \"" + url + "\"", e);
            return null;
        }
    }

}