Katie,
Are you ready to try something different? Internet Explorer 9 allows to configure what should happen when content is delivered without expiration information. Let's see if we can use this to fix the problem.
Please go inside Tools > Internet Options > Browsing history > Settings. See the screenshots for help.
Under "Check for newer versions of stored pages" choose "Every time I visit the website". Then click on OK to close the dialog button and
restart Internet Explorer. Now go to
https://www.mobileread.com/forums/usercp.php and see if it worked.
Either way, afterwards you can go back to Tools > Internet Options > Browsing history > Settings and change "Check for newer versions of stored pages" back to "Automatically".