"The EntityReference Object Could Not Be Serialized" When Serializing From .NET Web Site,?

I have an Entity Framework data model. Part of the model is a Customer entity. The web service provides a method to get a customer, and to receive an updated version of this customer to be persisted.

To test this, I created a new ASP.NET web Application, (Solution > Add > New Project > ASP.NET Web Application), then added a reference to my service reference using the standard Add Service Reference dialog. I then call the service using the following code:

var client = new CustomerServiceClient();
var customer = client.GetCustomerByID(18); // get it
customer.LimitDown = 100; // change it
client.SaveCustomer(customer); // persist it


Everything works as expected.

Now, I do exactly the same thing, but this time with as ASP.NET Web Site (Solution > Add > New Web Site > ASP.NET Web Site). I add the reference in a similar fashion and copy and paste the code above into the new site. But now I get the following exception thrown on the 4th line:

System.InvalidOperationException The EntityReference object could not be serialized. This type of object cannot be serialized when t RelationshipManager belongs to an entity object that does not implement IEntityWithRelationships.

Source Error:

Line 2474: Line 2475:
public
SkyWalkerCustomerService.OperationResult
SaveCustomer(SkyWalkerCustomerService.Customer[code]....

Googling for this error returns very little. Why doesn't this work?I guess one answer would be to use a web application instead of a web site, but I have an large existing site to which I need to add the service reference, and I'd rather not convert it.