Check your plog-config.php file and that it wasn't deleted accidentally (I don't know why this would be). Also, check with your webhost that they did not upgrade their sql site so now the location moved from 'localhost' to 'sql.yoursite.com' or something simliar.
This notice usually shows up when Plogger cannot connect to the sql database.
okay ... so what's in your plog-config.php? Don't post the actual settings here sinct they may contain passwords, but can you verify that there is something set for define("PLOGGER_DB_HOST", "your_host_here"); ?
Also, can you let us know if you are running the beta3 version or a newer SVN version?