Error : Cannot add an entity with a key that is already in use, when using ExecuteCommand

Question

I deleted a record by using ExecuteCommand between Linq to SQL insertions as below.

At the last call of SubmitChanges, I got below error :

Cannot add an entity with a key that is already in use.

If I use Linq to SQL for deleting, I get no problem, but ExecuteCommand is a released code, so I can't change it.

How should I insert deleted record again ?

Below is my Code :

Using db = New SomeDataContext(...)

    db.Connection.Open()
    db.Transaction = db.Connection.BeginTransaction()

    ' Insert
    db.Student.InsertOnSubmit(New Student() With {.Id = 1, .Name = "a"})
    db.SubmitChanges()

    ' Delete(ExecuteCommand)
    db.ExecuteCommand("delete from Student where Id = 1")
    db.SubmitChanges()

    '' Delete(Linq to SQL)
    'db.Student.DeleteOnSubmit(db.Student.Single(Function(m) m.Id = 1))
    'db.SubmitChanges()

    ' Insert
    db.Student.InsertOnSubmit(New Student() With {.Id = 1, .Name = "a"})
    db.SubmitChanges()
End Using

I am using Visual Studio 2013 with SQL Server access.