Change your navigation menu to a text-based navigation menu to avoid compatibility issues in IE8. To do this, click on each page, open the Inspector window, navigate to the "Page" tab and uncheck the "Include Page In Navigation Menu" option.
On one of the pages, click the "Text Box" button, enter the text that will act as an anchor, resize the text box and move it to the navigation menu. Select the anchor text and press the "Inspector" button. Navigate to the tab with a blue circle on it, select the "Enable as Hyperlink" option and enter the page's URL. Do this for all the links you want on your navigation menu.
Hold the "Ctrl" key and select each text box. Press the "Ctrl" and "C" keys simultaneously to copy the navigation menu. Go to each page and press the "Ctrl" and "V" keys simultaneously to paste the navigation box. You now have a text-based navigation menu on each of your pages.