Urgent fix db mysql

Hello i cannot access plesk but i can access ftp. On website [login to view URL] you see this error jtablesession::Store Failed DB function failed with error number 1062 Duplicate entry '1-' for key 'whosonline' SQL=INSERT INTO `jos_session` ( `session_id`,`time`,`username`,`gid`,`guest`,`client_id` ) VALUES ( 'r7s5amhtl9nqebe7f4ivl40127','1369372747','','0','1','0' ) Are you available to fix it now and let me know what is the problem if ever, and fix it so this don't happens again? THanks Please accept only if you can start now.