Solutions to Frequently Asked Questions
  
Question: Why do I get "Page Expired" notices when I use the browsers back button?
  
Answer:  This means that your browser cache is full. You will need to periodically clear your cache to prevent this from happening.

To clear your cache if you are using Internet Explorer, do the following steps. From your main menu, select "Tools", Internet Options", and then "Delete Files...". (Make sure you check the box to delete offline content), then select "Ok".

Depending on how long it has been since you last cleared your cache, this may take a few minutes to complete. If you clear your cache on a weekly basis, it will not take as long to clear the cache.

There is also a support article on the Microsoft website that you may wish to read that also addresses this problem, and suggests a service pack upgrade for Internet Explorer users.