Telerik 2014.2.618.35 2014 Q2 Walkthrough
1- Fix Html Bugs
a) no "not opened tag", no "not closed tag" etc., 
b) same width for the same <td> in different <tr>
c) no duplicate UniqueName   between  <columns></columns> tags
d) GridColumns'  DataFields must exist in the data source  ( is DataField is set to ="XXX" , the datasource must have "XXX" field before the binding)
2- GridBoundColumn Property Tag Rename : Visible to Display
<telerik:GridBoundColumn DataField="BookingId" UniqueName="BookingId"  Visible="false"   Display="false">
(Visible="false" columns are no more in the view state)
3- <GridBoundColumn… Display=false >
a) Number of these columns must fewer than other columns number.
b) These columns must be stated at bottom of <columns></columns> block
4- Web Config Settings
Add /  Change
<appSettings>
    <add key="Telerik.Grid.Skin" value="2011"/>
    <add key="Telerik.Grid.EnableEmbeddedSkins" value="false"/>
    <add key="Telerik.GridFilterMenu.Skin" value="2011"/>
    <add key="Telerik.GridFilterMenu.EnableEmbeddedSkins" value="false"/>
    <add key="Telerik.Dock.Skin" value="Yna"/>
..
..
..
<controls>
        <add tagPrefix="telerik" namespace="Telerik.Web.UI" assembly="Telerik.Web.UI, Version=2014.2.618.35, Culture=neutral, PublicKeyToken=121fae78165ba3d4"/>
      </controls>
 
5- if the GridExpandColumn does  not rendered properly
protected void BookingListesiGridView_ColumnCreated(object sender, GridColumnCreatedEventArgs e)
        {
            if (e.Column.ColumnType == "GridExpandColumn")
            {
                e.Column.HeaderStyle.Width = Unit.Pixel(35);
            }
        }
6- RadUpload ContentLenght property is long now. You may need to remove, change or add  the "conversion" code.
7 -Test your pages for different ie versions especially for Document mode 7 (f12 developer tools)