I have been using umbraco for some time, but there is something that is troublming me.  Every once and a while a site will go down, I will delete the contents of the app_data folder and it comes back up.  I don't mind doing this to fix the site, but I don't know why it is happening in the first place.  I get told the site is down, and I put it back up. Is there any way to find the problem or prevent the problem from happening? It seems to always fix with an app_data clearing no matter what the problem.