MBPM Web Client add custom button to the main screen

Hi, i'm trying to add a custom button for open a web page into homescreen on MBPM (9.2.1).

I have followed "Web client administration guide" paragraphs:

1.30 (Adding Custom Buttons)
1.32 (Display the contents of an external site)
I've also trapped the ListType exception in Default.aspx.cs:
try { ListType = listType.Value; } catch (Exception ex) {}

After doing this, i'm seeing the new button in my web client homescreen, but when i click on the button it load the same functionality (todolist, watchlist,...) already opened in web client.

This is Default.aspx.cs:

PlaceHolder helpPageHolder = new PlaceHolder();
helpPageHolder.ID = "helpPageHolder";
contentArea.Controls.Add(helpPageHolder);
// ...
listType = BaseListPart.GetListType(checkedGroupButton.CommandName);
            try { ListType = listType.Value; } catch (Exception ex) {}
            switch (listType)
            {
// ... others placeholders
default:
                    // Put here logic for any custom content.
                    if (!(currentControl is ContentViewer))
                    {
                        ContentViewer myViewer = new ContentViewer();
                        myViewer = new ContentViewer() { Location = "http://www.google.com" };
                        myViewer.Enabled = true;
                        newControl = myViewer;
                        newControl.ID = newControl.GetType().Name + "_" + checkedGroupButton.CommandArgument;
                        helpPageHolder.Controls.Add(newControl);
                    }
                    break;

This is Default.aspx:

<telerik:RadToolBarButton SkinID="NavHelpPage" CheckOnClick="false" Group="NavItems"
                    CommandName="HelpPage" Text="Help" ToolTip="Help page" />

This is Default.skin:

<telerik:RadToolBarButton skinid="NavHelpPage" CssClass="rtbMain" CheckedCssClass="rtbMainChecked" HoveredCssClass="rtbMainHovered" imageurl="Images/ListButtons/icn_help_custom.png" ImagePosition="Left" runat="server" />