Uncaught TypeError: Cannot read property 'UI' of undefined

Question

The error is in an ASP.NET Ajax application. This is the line of JQuery UI code the error refers to:

Sys.Extended.UI.DropDownBehavior

Answer 1

<ajaxToolkit:ToolkitScriptManager ID="ScriptManager1" runat="server"></ajaxToolkit:ToolkitScriptManager>

use it instead of simple script manager

Answer 2

The solution was to replace <asp:ScriptManager> with <ajaxToolkit:ToolkitScriptManager>.

Answer 3

In my case, I ended up needing to use <ajaxToolkit:ToolkitScriptManager> instead.