Errata

product class Product {
...
public int QuantityPerUnit {
...
}

should be

product class Product {
...
public string QuantityPerUnit
...
}

to be used with the example data ;-)

The code for the property of the class:
public int CustomerId
{
get { return _customerId; }
set { _customerId = value; }
}

Missing one line of tag. According to the description in page 132, it should be like

[DataMember]
public int CustomerId
{
get { return _customerId; }
set { _customerId = value; }
}

Also for VB code, one line as
<DataMember> _

need to be added for the property CustomerId too.

The line is:
when user click the OK button. Figure 6-2 shows the Silverlight 2 user interface

It should be read as:
when user click the Save button. Figure 6-2 shows the Silverlight 2 user interface