Error:

Problem:

By default “Spell check” button uses “AjaxSpellCheck” not “SpellCheck “

  <telerik:EditorTool Name="SpellCheck" Enabled="true" />

Solution:

Use AjaxSpellchek

   <telerik:EditorTool Name="AjaxSpellCheck" Enabled="true" />

Problem:

RadEditor Content not saved on page postback.

Solution:

Add UseSubmitBehavior="false" to the button that’s causing page postback.

<asp:Button ID="Button1" runat="server" 
OnClick="Button1_Click" Text="Button1"  UseSubmitBehavior="false"  />