Hessian uses v1 as default. It will give you error in the case you're using. However, HessianProxyFactory can be easily switched to v2 mode, like I demonstrate here in the following sample code:
HessianProxyFactory factory = new HessianProxyFactory();
factory.setHessian2Request(true);
// Do something
Source: Hessdroid
Hope that will work for you!