The probable culprit is an outdated web browser. Make sure you have a current version. On Windows, the site works best using Internet Explorer 8 or newer; with Apple, the site works best using Sarfari 5 or newer.
 
If you have an updated web browser, it may be that the cache setting needs to be changed. On your browser menu bar, go to Tools and click on “Internet Options.” From the “General” tab in the “Browsing history” section, click on the “Settings” button. Chose the option shown below: