Recently we had a client's website that suddenly went down for no apparent reason.  The server was up and running mysql was functioning but, we couldn't bring up the application software on the website.  I began investigating it early on a Friday morning by first following the error reporting to a file to see what was it that it was apparently trying to do and couldn't.  After a frustrating few hours and for some reason I was looking at the data tables and noticed that it all appeared to be corrupt or missing data.  Well to make a long story short, it ran into Saturday morning before I finally realized what had happened.  The application software this client was using is very intelligent.   One of the functions the application performs when it is called upon is to look at the data tables and make sure it is the correct version for the version of the application running.  It's part of the upgrade function, whenever you upgrade the application to the newer version it will then check the data tables to see if it has been updated and if not update them to the newer version.  The problem is even if you hadn't updated the application, whenever you call the program it checks the data tables for the correct version.  Well, for some reason it did it's check and decided this time the tables need to be updated.  However, it decided to not update if from the last version to the version it was using but to start with the very first upgrade version, like eleven upgrades back and that's what created the problem.