[vb.net]DataGrid probleme evenement

Bonjour tout le monde,
je suis face a un problème peut être très bête mais je ne sais pas le résoudre.
Je dispose d'un datagrid créé dans mon code, et je dois lui affecté un evenement pour que quand l'utilisateur selectionne une des lignes vides (qui simule des cases a cocher) ca inscrive un "X" dedans. Mais ca marche pas :(
Voici mon code pour l'evenement

Code:

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    Public Sub data_grid_CurrentCellChanged(ByVal sender As Object, ByVal e As MouseEventArgs) Handles data_grid.CurrentCellChanged

        If data_grid.CurrentCell.ColumnNumber = 4 Then
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber) = "X"
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber + 1) = ""
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber + 2) = ""
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber + 3) = ""

        ElseIf data_grid.CurrentCell.ColumnNumber = 5 Then
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber - 1) = ""
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber) = "X"
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber + 1) = ""
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber + 2) = ""

        ElseIf data_grid.CurrentCell.ColumnNumber = 6 Then
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber - 2) = ""
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber - 1) = ""
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber) = "X"
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber + 1) = ""

        Else
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber - 3) = ""
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber - 2) = ""
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber - 1) = ""
            data_grid.Item(data_grid.CurrentCell.RowNumber, data_grid.CurrentCell.ColumnNumber) = "X"
        End If
    End Sub          'rempli les cases a cocher du data grid avec des X

L'erreur est affiché pour le data_grid en rouge
D'avance merci

Nasty