Site is "Temporarily Unavailable" I get "Service Unavailable" when I go to my (hosted, not local) test site. 

It had been working just fine until I decided to swap databases today.

I deleted the old database and replaced it with the new database.  I kept the database name the same.  I changed the username and password in cPanel and then duplicated those changes in my craft/db.php file... But no dice...  I get the nice little warning:


  Service Unavailable 
  
  Our site is temporarily unavailable.  Please try again later.


I have checked more than once, the path, db name, username and password all check out.  Any suggestions?  ...other than start over
Others have said what the problem is, but in the interest of clarity for future readers...

Cause: The database is expecting a newer version of Craft's filesystem than you have.

Solution: Replace the /app folder with one from a fresh Craft download and visit your admin trigger URL