CellContentDoubleClick does not fire when you for instance also place a DoDragDrop-statement in a MouseDown eventhandler for the datagridview.
Here is the code I have, that causes CellContentDoubleClick not to fire (the cause is here emphasized in boldface):
Private Sub gridd_MouseDown(sender As Object, e As System.Windows.Forms.MouseEventArgs) Handles gridd.MouseDown
SourceRowIndex = -1
SourceColIndex = -1
If e.Button = Windows.Forms.MouseButtons.Left Then
If gridd.HitTest(e.X, e.Y).Type = DataGridViewHitTestType.Cell Then
SourceRowIndex = gridd.HitTest(e.X, e.Y).RowIndex
SourceColIndex = gridd.HitTest(e.X, e.Y).ColumnIndex
DoDragDrop(gridd.Rows(SourceRowIndex).Cells(SourceColIndex).Value, DragDropEffects.Copy)
End If
End If
End Sub
This line is causing the problem (at least in my case):
DoDragDrop(gridd.Rows(SourceRowIndex).Cells(SourceColIndex).Value, DragDropEffects.Copy)