Could be anything.
Usually it is a issue with connecting to the database.
Host issue.
FYI,
That is a generic message.
You could try the host cp and look for errors.
Or edit the mysql.inc.php file and enable messages to display on the browser.
This is not recommended to leave enabled.
Due to it displays paths on your server.
// IF YOU SET THE VARIABLE BELOW TO 1 IT WILL SHOW THE SQL ERRORS TO ALL
// USERS. USEFUL IF YOU CANNOT LOG IN AND NEED TO SEE THE SQL ERRORS
$showerror = 0;
change the showerror value from a 0 to a 1