All the settings were fine and I was wondering what’s causing the problem. At first rush I thought that it could be a cache, as I had requested recently to have xcache on our server.
But it wasn’t the case. The error was much more stupid than even one can imagine. That specific script uses a stored procedure to insert / fetch data to/from MySQL. The user who had created the sp was the one who was deleted. And that was the problem. The term “Definer” in terms of MySQL is the one who creates the stored procedure and for the stored procedure to be executed that user must exists.
http://stackoverflow.com/questions/2398368/what-exactly-this-error-is