Question

“Only one instance of a ScriptManager can be added to the page.” this error appear when I added the script Manager to the password strength of AJAX toolkit.

i added the password strength beside the password field of my createuserwizard.
why this error would appear when this is the only scriptmanager that i had in my website?

here is the code:

 <asp:TextBox runat="server" ID="Password" TextMode="Password" MaxLength="20" />
<asp:ScriptManager ID="ScriptManager2" runat="server">
</asp:ScriptManager>
 <asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate> 
 <asp:PasswordStrength ID="Password_PasswordStrength" runat="server" 
                                Enabled="True" TargetControlID="Password"   DisplayPosition="RightSide"
                             StrengthIndicatorType="BarIndicator"
                              BarBorderCssClass="barBorder"
                               BarIndicatorCssClass="barInternal">
                         </asp:PasswordStrength>

                            <asp:RequiredFieldValidator runat="server" ID="RequiredFieldValidator10" ControlToValidate="Password" 
                                ErrorMessage="Password is required." />   
      </ContentTemplate> </asp:UpdatePanel> 
                        </td>
                    </tr>

Answer 1

Just remove this ScriptManager and it will work fine.

<asp:ScriptManager ID="ScriptManager2" runat="server">
</asp:ScriptManager>

You have definitely added a ScriptManager somewhere else in your Page or MasterPage.

ScriptManager Control Overview

Only one instance of the ScriptManager control can be added to the
page. The page can include the control directly, or indirectly inside
a nested component such as a user control, content page for a master
page, or nested master page. If a page already contains a
ScriptManager control, but a nested or parent component needs
additional features of the ScriptManager control, the component can
include a ScriptManagerProxy control. For example, the
ScriptManagerProxy control enables you to add scripts and services
that are specific to nested components.