Your browser will cache anything it downloads so that if you go to the same site again, it doesn't need to download it again.
First try IFR's solution, which makes sure that your PPRuNe cookie is properly set up. If that doesn't fix the problem, then you need to tell your browser that it should check to see if a web page has been updated every time it visits a page. How you do this depends on your browser.
For Internet Explorer 5, click on the Tools/Internet Options... menu item.
Then click on Settings (which is in the Temporary Internet file part of the window)
Then make sure Check for newer version of stored pages :"Every visit to the page" is clicked.
If you are using some other browser, then you'll have to RTFM (Read The Friendly Manual)
--PPD