DataSet not defined

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    Dim AppName As String = Session("App_Name").ToString()
    Dim username As String = Session("username").ToString()
    Dim password As String = Session("password").ToString()
    Dim ds As DataSet = GContactsImport.GetGmailContacts(AppName, username, password)
    GridView1.DataSource = ds
    GridView1.DataBind()


End Sub

how do i fix it??

This is my class file

Imports Microsoft.VisualBasic
Imports Google.GData.Contacts
Imports Google.GData.Client
Imports Google.GData.Extensions
Imports Google.Contacts

Public Class Google
Public Shared Function GetGmailContacts(ByVal AppName As String, ByVal Uname As String, ByVal UPassword As String) As DataSet
Dim ds As New DataSet()
Dim dt As New DataTable()
Dim C2 As New DataColumn()
C2.DataType = Type.GetType
C2.ColumnName = "EmailID"
dt.Columns.Add(C2)
Dim rs As New RequestSettings(AppName, Uname, UPassword)
rs.AutoPaging = True
Dim cr As New ContactsRequest(rs)
Dim f As Feed(Of Contact) = cr.GetContacts()
For Each t As Contact In f.Entries
For Each email As EMail In t.Emails
Dim dr1 As DataRow = dt.NewRow()
dr1("EmailID") = email.Address.ToString()
dt.Rows.Add(dr1)
Next
Next
ds.Tables.Add(dt)
Return ds
End Function

End Class