A new feature has been added in Moodle 1.5 to track read/unread forum posts.  To use this functionality you need to update your tables with all the tracking information for existing posts.  Depending on the size of your site this can take a long time (hours) and can be quite taxing on the database, so it's best to do it during a quiet period.  However, your site will continue functioning during this upgrade and users won't be affected.  Once you start this process you should let it finish (keep your browser window open).  However, if you stop the process by closing the window: don't worry, you can start over.<br /><br />Do you want to start the upgrading process now?