Private Sub DataGridView1_CellEndEdit(ByVal sender As Object, ByVal e As _
  System.Windows.Forms.DataGridViewCellEventArgs) Handles _
  DataGridView1.CellEndEdit

Dim Text as string = Me.DataGridView1.CurrentCell.Value
if Text.contains(Buchstaben und Sonderzeichen) then
  Msgbox("Bitte nur Zahlen verwenden")
  Exit sub