Please see my post here
. If you are experiencing the same issue, the cause could be that either your grid's ID starts with an underscore, or any of the parent control's ID starts with an underscore. Parent controls can be the Master Page's ContentPlaceHolder or any control which the grid is nested inside.
As you saw on this thread, Telerik says that the issue will be fixed. But when I submitted a bug report, with a complete patch of the source, they responded that the problem was too hard to fix.
I recommend changing your IDs to not start with underscores.