Update Panel isn't rendering correctly

Hello,

I am facing a very weird scenario lately. I have page that uses several update panels, which some of them are nested inside of the others.

Each update panel is using ChildrenAsTriggers="False" and  UpdateMode="Conditional".

The main Update Panel wraps a RadGrid control (Telerik control for DataGrid) .

Inside the EditFormTemplate of this control , I have another UserControl that imports data from a WCF service and display it.

Until now, this site was published in Server2003 , and lately we published it on another server using Server2012.

The problem is that in the new server (Server 2012) , the update panel stop rendering after opening some of the rows to edit mode.

The weird thing is that when I open firebug , to see the traffic , I can see that the request are send and received with no error.

More over, I couldn't find a common scenario for rows that are failed to open . Some times that page freeze after 5 successful attempts , and sometimes after 7 or 10.
Sometimes after the page freeze ,I can open another rows , and some times I can't.

Also, some times a specific attempt to open the same row for edit is successful  and sometimes it doesn't ,but all the time the traffic is being sent and received correctly.

Any help will be appreciated,

Kind regards,

Tal Humy