Note: It appears that your database may require an upgrade. Your forum's files are currently at version SMF 2.0.15, while your database is at version 2.0.3. The above error might possibly go away if you execute the latest version of upgrade.php.
Does it say anything else?
Do you get an email with the error information?
what is the error above that line? there are no database changes so an upgrade is not going to fix the issue.
Database Error
Incorrect key file for table './fronteng_smf/smf_log_online.MYI'; try to repair it
File: /home/fronteng/public_html/forum/Sources/Subs.php
Line: 2697
Note: It appears that your database may require an upgrade. Your forum's files are currently at version SMF 2.0.15, while your database is at version 2.0.3. The above error might possibly go away if you execute the latest version of upgrade.php.
Try to run this sql query on your database
REPAIR TABLE smf_log_online;
If not we might have to rebuild/recreate that table.
Restored to an earlier date and all seems well for the moment.