VS2008, IG controls 7.1, .NET 2.

I have an UltraWebToolbar control on the form with 4 buttons (the control is inside a WARP) -

                                       <igtbar:UltraWebToolbar ID="tbAdv" Width="200" runat="server" OnButtonClicked="tbAdv_ButtonClicked">
                                        <Items>
                                          <igtbar:TBarButton Image="opendir.gif" Text="Open" Key="open">
                                            <Images>
                                              <DefaultImage Url="opendir.gif" />
                                            </Images>
                                            <DefaultStyle CssClass="tb_d" Width="56px">
                                            </DefaultStyle>
                                          </igtbar:TBarButton>
                                          <igtbar:TBarButton Image="save.gif" Text="Save" Key="save">
                                            <Images>
                                              <DefaultImage Url="save.gif" />
                                            </Images>
                                            <DefaultStyle CssClass="tb_d" Width="56px">
                                            </DefaultStyle>
                                          </igtbar:TBarButton>
                                          <igtbar:TBarButton Image="Save.gif" Text="Save as..." Key="saveas">
                                            <Images>
                                              <DefaultImage Url="Save.gif" />
                                            </Images>
                                            <DefaultStyle CssClass="tb_d" Width="80px">
                                            </DefaultStyle>
                                          </igtbar:TBarButton>
                                          <igtbar:TBarButton Image="find.gif" Text="New" Key="new">
                                            <Images>
                                              <DefaultImage Url="find.gif" />
                                            </Images>
                                            <DefaultStyle CssClass="tb_d" Width="56px">
                                            </DefaultStyle>
                                          </igtbar:TBarButton>
                                        </Items>
                                      </igtbar:UltraWebToolbar>
 

Clicking on any of the buttons gives a javascript error like the following -

Line: 69692273
Error: Syntax error 

The line number is random but is usually in the millions! Clicking 'Yes' to debug just clears the error (it won't debug). The button click does post back and the error appears after it has.

EDIT: Adding <xhtmlConformance mode="Legacy"> to the web.config seems to fix it, but this isn't ideal...