R – Silverlight WCF access returning an IList of LLBLGen entities

I'm having a problem passing an entity collection back from LLBLGen to silverlight. My contract looks like this. I don't even know if this is possible.

My web service code looks like this:

public IEnumerable<WaterWorksCustomersEntity> GetCustomer(long custId, string acctKey)
{
    var toReturn = new WaterWorksCustomersEntity(custId, acctKey);
    using (var adapter = new DataAccessAdapter())
    {
        adapter.ConnectionString = "data source=CWCPROD.cwc.local;user.."; 
        adapter.FetchEntity(toReturn);
    }
    IList<WaterWorksCustomersEntity> customers = new List<WaterWorksCustomersEntity>();
    customers.Add(toReturn);
    return customers; 
}

On the silverlight client I'm doing …

var client = new Service1Client();
client.GetCustomerCompleted += new EventHandler<GetCustomerCompletedEventArgs>(client_GetCustomerCompleted);
client.GetCustomerAsync(2,"110865");

The compilation is failing with this error:

Error 1 The type or namespace name 'ArrayOfXElement' does not exist in the namespace 'AppointmentClientSL.ServiceReference1' (are you missing an assembly reference?) c:\work\Appointment\Appointment\AppointmentClientSL\Service
References\ServiceReference1\Reference.cs 63 54 AppointmentClientSL

It looks like SL is not able to deal with the data the web service is returning.

Can anyone help???