RadTextBox in RadWindow

[JS]

Hi There,

When placing a RadTextBox inside a RadWindow, I get a JavaScript Error: TypeError: $telerik.$ is undefined

Placing a RadComboBox works without any problems.

This is my code:

<telerik:RadWindow ID="Details" runat="server" Title="Details" Width="450" Height="536"
 VisibleOnPageLoad="false" Behaviors="Move, Close" Left="580" EnableShadow="true" RegisterWithScriptManager="false">
    <ContentTemplate>
             <telerik:RadTextBox ID="Test" runat="server">
             </telerik:RadTextBox>
    </ContentTemplate>
</telerik:RadWindow>

Is this a know bug?

*UPDATE*

My bad, RegisterWithScriptManager="false" caused this behaviour.