This is the error message I keep getting even after I upgraded the program;
Incorrect key file for table './neweng26_smf1/smf_log_online.MYI'; try to repair it
File: /home/neweng26/public_html/SMF/Sources/Subs.php
Line: 2583
Note: It appears that your database may require an upgrade. Your forum's files are currently at version SMF 1.1.13, while your database is at version 1.1.11. The above error might possibly go away if you execute the latest version of upgrade.php.
I have seen a similar error posted on these forums a few times recently.
http://www.simplemachines.org/community/index.php?topic=436430.msg3063035#msg3063035
This MIGHT help you.
This is more specific for the error you're getting:
http://www.simplemachines.org/community/index.php?topic=275098.0
If a repair of the smf_log_online table should fail, it is also relativily safe to Truncate that table (but NOT just any table).