WCF / ASMX :: Linq To SQL Web Service Cannot Be Serialized?

I'm playing around with Web Services using Linq to SQl. I apparently have a lot of learning to do. What I'm trying to do below is pull data from the Northwind db Employee Table. I don't need to see the whole table, I'm just trying to select individual(s) but I keep getting the following error

"System.Data.Linq.Binary cannot be serialized because it does not have a parameterless constructor"

Code Below:

<WebMethod()> _
Public
Function EmployeeInfo()
As List(Of Employee)
Dim db
As
New NorthwindDataContext()
Dim output =
From cust
In db.Employees _
Select cust.EmployeeID, cust.FirstName, cust.LastName
Return output
End
Function