Hi Fabrício,

I upgraded to Ext.NET 5.3. So far it works. But now it loses the selection when I work with grouping. Here is the new code.

Imports Ext.Net

Public Class grid2

    Inherits System.Web.UI.Page

    Dim aktGrid As New GridPanel

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        Dim aktResourceManager As New ResourceManager
        With aktResourceManager
            .ID = "rm"
            .Theme = Ext.Net.Theme.Neptune
        End With

        With aktGrid

            .ID = "mwgrid"
            .Width = 700
            .Height = 350


            .EnableLocking = True

            Dim _Store As New Store
            _Store.ID = "store1"

            Dim _Model As New Model

            _Model.IDProperty = "Col1"

            For i As Integer = 1 To 10

                If i = 1 Then
                    _Model.Fields.Add(New ModelField("Col" & i.ToString, ModelFieldType.Int))
                    _Model.Fields.Add(New ModelField("Col" & i.ToString, ModelFieldType.String))
                End If



            _Store.DataSource = Me.Data


            With .ColumnModel

                For i As Integer = 1 To 10

                    Dim _Col As Object

                    If i = 1 Then
                        _Col = New NumberColumn
                        _Col = New Column
                    End If

                    _Col.ID = "Col" & i.ToString
                    _Col.Text = "Col" & i.ToString
                    _Col.DataIndex = "Col" & i.ToString

                    If i = 1 Then _Col.Locked = True



            End With

            Dim _RowSelModel As New RowSelectionModel

            With _RowSelModel
                .Mode = SelectionMode.Single
            End With


            .Features.Add(New Grouping)

            Dim _View As New GridView
            _View.StripeRows = True
            _View.TrackOver = True


        End With

        Dim _button As New Button("Databind")
        AddHandler _button.DirectEvents.Click.Event, AddressOf Click
        _button.ID = "databind"


        If Not Ext.Net.ExtNet.IsAjaxRequest Then

            aktGrid.Store(0).GroupField = "Col2"

            Dim RM As RowSelectionModel = aktGrid.GetSelectionModel
            If RM.SelectedRows.Count = 0 Then
                RM.SelectedRows.Add(New SelectedRow(5))
            End If

        End If

    End Sub

    Private Sub Click(sender As Object, e As DirectEventArgs)


    End Sub

    Private ReadOnly Property Data As Object()

            Data = New Object() {New Object() {1, "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1"},
            New Object() {2, "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1"},
            New Object() {3, "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1"},
            New Object() {4, "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1"},
            New Object() {5, "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1"},
            New Object() {6, "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1"},
            New Object() {7, "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1"},
            New Object() {8, "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1"},
            New Object() {9, "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1"},
            New Object() {10, "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1"},
            New Object() {11, "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1", "test1"}}

        End Get

    End Property

End Class