SplitterPane has EnableRelativeLayout property that needs to be set to true to display properly in IE8 Compatible Mode.

<ig:WebSplitter ID="WebSplitter1" runat="server" Height="200px" Width="300px" DynamicResize="True">
            <ClientEvents SplitterBarMoving="WebSplitter1_SplitterBarMoving" />
            <Panes>
                <ig:SplitterPane runat="server" EnableRelativeLayout="true">
                    <Template>
                        <ig:WebProgressBar ID="WebProgressBar1" runat="server" Maximum="300"
                            Value="150">
                        </ig:WebProgressBar>
                    </Template>
                </ig:SplitterPane>
                <ig:SplitterPane runat="server">
                </ig:SplitterPane>
            </Panes>
        </ig:WebSplitter>

Please let me know if this is working for you.

Hello Alejandro,

you can put the progress bar where you want, it will not change its size. It shows you the progress when you change the size of the splitter panel.

Please let me know if you need additional assistance

Is there another solution? because this is not suitable for my case, my client don't want to change the apperance of the page, besides is not an elegant solution from the estetic point of view, I don't want the progress bar resizes with the container panel.