Есть класс:

Imports System.Data.SqlClient

Public Class Author
    Private cnPubs As SqlConnection
    Private daPubs As SqlDataAdapter
    Private dsPubs As DataSet

    Public Sub New()
        cnPubs = New SqlConnection()
        cnPubs.ConnectionString = _
            ("Integrated Security=True; Data Source=LocalHost; Initial Catalog=Pubs")
        Dim strSQL As String
        Dim oSelCmd As SqlCommand
        strSQL = "SELECT au_id, au_lname, au_fname FROM authors"
        oSelCmd = New SqlCommand(strSQL, cnPubs)
        daPubs = New SqlDataAdapter()
        daPubs.SelectCommand = oSelCmd

        Dim oUpdCmd As SqlCommand
        strSQL = "UPDATE authors set au_lname = @au_lname, au_fname = @au_fname, WHERE au_id = @au_id"
        oUpdCmd = New SqlCommand(strSQL, cnPubs)
        oUpdCmd.Parameters.Add("@au_id", SqlDbType.VarChar, 11, "au_id")
        oUpdCmd.Parameters.Add("@au_lname", SqlDbType.VarChar, 40, "au_lname")
        oUpdCmd.Parameters.Add("@au_fname", SqlDbType.VarChar, 40, "au_fname")
        daPubs.UpdateCommand = oUpdCmd
    End Sub

    Public Function GetData() As DataSet
        dsPubs = New DataSet()
        daPubs.Fill(dsPubs, "Authors")
        Return dsPubs
    End Function

    Public Function UpdateData(ByVal DSChanged As DataSet) As Boolean
        Try
            daPubs.Update(DSChanged, "Authors")
            Return True
        Catch ex As Exception
            Return False
        End Try
    End Function
End Class

Почему-то функция GetData() — работает
а функция UpdateData() — не работает и возвращает False
Может кто-нибудь подскажет, почему?