To reproduce:
public RadForm1()
{
    InitializeComponent();
    radVirtualGrid1.CellValueNeeded += RadVirtualGrid1_CellValueNeeded;
    radVirtualGrid1.ColumnCount = 100;
    radVirtualGrid1.RowCount = 50;
    radVirtualGrid1.AutoSizeColumnsMode = Telerik.WinControls.UI.VirtualGridAutoSizeColumnsMode.Fill;
    radVirtualGrid1.SelectionMode = Telerik.WinControls.UI.VirtualGridSelectionMode.CellSelect;
}

private void RadVirtualGrid1_CellValueNeeded(object sender, Telerik.WinControls.UI.VirtualGridCellValueNeededEventArgs e)
{
    e.Value = string.Format("Col {0} Row{1}", e.ColumnIndex, e.RowIndex);
}