ASPNetSpell has native support for ASP.Net AJAX. To get the most out of this - when Installing ASPNetSpell use the AJAX ready version of the DLL.
ASPNetSpell also works with the ASP.NET AJAX Control Toolkit.
For best integration - we suggest that you move the ToolkitScriptManager To the end of your form, rather than the start. This works around an apparent bug in the TabContainer component.SourceCode:
<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server"></asp:ToolkitScriptManager>