Panel fail to be visible

I coded a pop up panel but it can't seems to be visible even when i " Panelpopup.visible =true;" 
I tried to put this(" Panelpopup.visible =true;" ) into another button and it worked fine. Please help me ! 
protected void btnDel_Click(object sender, EventArgs e) { // Calling method to bind grid view bindGridview1(); // Calling export method Export(); // Enable panel visibility PanelPopup2.Visible = true; }