I just updated my software and the software will work in the latest version but if I try to go back and use an older version, the software will not open.  I was able to use this version before I updated, why can I not use it now?

You may have updated to a new level of software that did not exist in previous versions.  For example, if you updated to Tajima Pulse Composer or Illustrator Extreme, you will not be able to use these levels in versions prior to version 2009.