I tried using the Infragistics.Win.DateTimeEditor object instead as follows but when double-clicking the cell editing behaves as if it were a text edit:

         UltraTree1.Nodes(0).SetCellValue(objSecondColumn, Now)
        UltraTree1.Nodes(0).Override.CellClickAction = Infragistics.Win.UltraWinTree.CellClickAction.EditCell
        UltraTree1.Nodes(0).Override.UseEditor = Infragistics.Win.DefaultableBoolean.True       
        UltraTree1.Nodes(0).Override.SelectionType = Infragistics.Win.UltraWinTree.SelectType.Single
        UltraTree1.Nodes(0).Override.ShowEditorButtons = Infragistics.Win.UltraWinTree.ShowEditorButtons.Always
        UltraTree1.Nodes(0).Override.Editor = New Infragistics.Win.DateTimeEditor ' <----

The following line displays "EditorWithText" instead of "DateTimeEditor":

MsgBox(TypeName(UltraTree1.Nodes(0).Cells(objSecondColumn).EditorResolved).ToString)

There is a little tricky solution, but I hope that exist another form to do it. Following your code, place a UltraDateTimeEditor1 in the Form1

In the Form1_Load event
      Dim objFirstColumn As Infragistics.Win.UltraWinTree.UltraTreeNodeColumn
      Dim objSecondColumn As Infragistics.Win.UltraWinTree.UltraTreeNodeColumn

      UltraTree1.ViewStyle = Infragistics.Win.UltraWinTree.ViewStyle.OutlookExpress
      UltraTree1.Override.UseEditor = Infragistics.Win.DefaultableBoolean.True
      UltraTree1.Override.LabelEdit = Infragistics.Win.DefaultableBoolean.True
      UltraTree1.Override.CellClickAction = Infragistics.Win.UltraWinTree.CellClickAction.EditCell

      objFirstColumn = UltraTree1.ColumnSettings.RootColumnSet.Columns.Add("Col1")
      objSecondColumn = UltraTree1.ColumnSettings.RootColumnSet.Columns.Add("Col2")

      UltraTree1.Nodes.Add("TestNode")
      UltraTree1.Nodes(0).SetCellValue(objFirstColumn, "Value11")
      UltraTree1.Nodes(0).SetCellValue(objSecondColumn, "Value12")

      'The Dock property must be Fill ***********
      UltraTree1.Dock = DockStyle.Fill

      objSecondColumn.AllowCellEdit = Infragistics.Win.UltraWinTree.AllowCellEdit.Full
      With UltraTree1.Nodes(0)
         .Override.CellClickAction = Infragistics.Win.UltraWinTree.CellClickAction.EditCell
         .Override.UseEditor = Infragistics.Win.DefaultableBoolean.True
         .Override.SelectionType = Infragistics.Win.UltraWinTree.SelectType.Single
         .Cells(objSecondColumn).EditorControl = UltraDateTimeEditor1
         .SetCellValue(objSecondColumn, Now)
      End With

      With UltraDateTimeEditor1
         .Visible = False
         .AllowDrop = True
         .AutoSize = True
      End With

      Me.UltraTree1.ColumnSettings.BorderStyleCell = Infragistics.Win.UIElementBorderStyle.Solid
      Me.UltraTree1.ColumnSettings.CellAppearance.BorderColor = SystemColors.Control

In the UltraTree1 BeforeCellActivate
      If TypeOf e.Cell.EditorControl Is Infragistics.Win.UltraWinEditors.UltraDateTimeEditor Then
         With UltraDateTimeEditor1
            .Height = e.Cell.UIElement.Rect.Height
            .Width = e.Cell.UIElement.Rect.Width
            .Top = e.Cell.UIElement.Rect.Location.Y
            .Left = e.Cell.UIElement.Rect.Location.X
            .Enabled = True
            .Visible = True
         End With
      Else
         UltraDateTimeEditor1.Enabled = False
         UltraDateTimeEditor1.Visible = False
      End If

In the UltraTree1 BeforeCellDeactivate
      If TypeOf e.Cell.EditorControl Is Infragistics.Win.UltraWinEditors.UltraDateTimeEditor Then
         e.Cell.Value = UltraDateTimeEditor1.Value
         UltraDateTimeEditor1.Enabled = False
         UltraDateTimeEditor1.Visible = False
      End If

Your are right: I can't have the DateTimeEditor to work, yet. I am quite frustrated.

But if you want to place or embeed other editors like DateTimeEditor or UltraNumericEditor in a specific cell, it works like you do? please tell me if it works to you

Thanks

Thanks, I got it working with the following code.

 By the way, how can I set an editor for a given cell? (that is, not for the entire column or the whole row).

I placed a new tree control on the form. In the form Load() event I wrote the following code:

        Dim objFirstColumn As Infragistics.Win.UltraWinTree.UltraTreeNodeColumn
        Dim objSecondColumn As Infragistics.Win.UltraWinTree.UltraTreeNodeColumn

        UltraTree1.ViewStyle = Infragistics.Win.UltraWinTree.ViewStyle.OutlookExpress
        UltraTree1.Override.UseEditor = Infragistics.Win.DefaultableBoolean.True
        UltraTree1.Override.LabelEdit = Infragistics.Win.DefaultableBoolean.True
        UltraTree1.Override.CellClickAction = Infragistics.Win.UltraWinTree.CellClickAction.EditCell

        objFirstColumn = UltraTree1.ColumnSettings.RootColumnSet.Columns.Add("Col1")
        objSecondColumn = UltraTree1.ColumnSettings.RootColumnSet.Columns.Add("Col2")

        UltraTree1.Nodes.Add("TestNode")
        UltraTree1.Nodes(0).SetCellValue(objFirstColumn, "Value11")
        UltraTree1.Nodes(0).SetCellValue(objSecondColumn, "Value12")

        objSecondColumn.AllowCellEdit = Infragistics.Win.UltraWinTree.AllowCellEdit.Full

        objSecondColumn.Editor = New Infragistics.Win.EditorWithText()

 Thanks a lot.