Problem to restore database backup..using smo server

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VB

Please help! I tried but cannot solve.

Here is the code I use is following:

Imports System.Data.SqlClient
Imports Microsoft.SqlServer.Management.Smo
Imports Microsoft.SqlServer.Management
Imports Microsoft.SqlServer.Management.Common
Imports Microsoft.SqlServer.Management.Sdk.Sfc
Imports System.Configuration

Dim db As String = ""
    Dim dbname As String = ""
    Dim con As New SqlConnection("Data Source=.\SQLEXPRESS;AttachDbFilename=C:\LandandBuildingProject\LandandBuildingProject\Building.mdf;Integrated Security=True;User Instance=True")
    Dim sqlserver As New Server(New ServerConnection(con))
    Dim WithEvents backup As New Backup
    Dim WithEvents restore As New Restore
    
    Sub dbrestore()
         If con.State = ConnectionState.Closed Then
            con.Open()
        End If

        Dim dbrest As New DatabaseUserAccess
        dbrest = DatabaseUserAccess.Single
        sqlserver.KillAllProcesses(db)


        db = ((ComboBox1.SelectedItem)).ToString

        restore.Database = db
 
        Dim device As New BackupDeviceItem(Openbakfile.FileName, DeviceType.File)
        restore.Devices.Add(device)

        restore.Action = RestoreActionType.Database

        ProgressBar2.Value = 0
        restore.PercentCompleteNotification = 10
        restore.SqlRestore(sqlserver)// error here
        con.Close()
        dbrest = DatabaseUserAccess.Multiple
        restore.Devices.Clear()
        
    End Sub

i get error of restore fail for server and Affinity Info = {"Failed to retrieve data for this request
thanks....