I'd also make sure that you try to log into mysql from the same computer as is running plogger.
mysql is really sensitive to where incoming connections are coming from so it may be allowing you to log in from one computer but not the other.
If this doesn't help, a little more information about your setup would help a lot such as are apache (the one running plogger) and mysql running on the same machine, how did you grant access to the database to the user you specify in plogger config and have you tried (successfully) to log into mysql with the mysql tools?