Collapsible Panel Smooth Animation - not working

Question

I have 2 Ajax collapsiblePanels one below the other. The first one has a repeater inside it and the second has a gridview. The JS function for both is exactly the same. The problem is, the animation is smooth for the second one, but not the first. I tried even setting extreme values for fps and duration, but not even a budge, as if they dont apply to it at all. What could be the reason.

JS:

function pageLoad()
{
  var collPanel = $find("<%=CollapsiblePanelExtender1.ClientID%>");
  if(!collPanel) {return;}
  collPanel._animation._fps=35;
  collPanel._animation._duration=0.3;
}

ASPX:

<div id="pHeader" runat="server" class="cpHeader">

  <span style="float:left"> History </span>
  <span style="float:right"><asp:Image id="imgArrows" runat="server" 
   width="17px" height="17px" ImageAlign="middle"/></span>
  <div style="clear:both"></div>
</div>

<asp:Panel id="pBody" runat="server" height="200px" width="100%" 
 scrollbars="vertical"  class="cpBody">

<asp:Repeater runat="server" id="rphistory">....</asp:repeater>
</asp:panel>

<asp:CollapsiblePanelExtender id="CollapsiblePanelExtender1" runat="server" 
 targetcontrolid="pBody" collapsecontrolid="pHeader"
expandcontrolid="pHeader" collapsed="true" collapsedsize="0"
 scrollcontents="false" imagecontrolid="imgArrows" 
  expandedimage="~/Images/expand.jpg" collapsedimage="~/Images/collapse.jpg">
</asp:CollapsiblePanelExtender>

Answer 1

How large is the GridView?

It could be caused by the fact that the GridView is essentially a bunch of HTML tags that build a table. If the table is very large the browser has to wait to render the entire table (the entire table must be rendered (even if hidden from the user) first) - then the animation should clean smooth