I found a message saying something like this at the Joomla! forums:
My site is hosted through Yahoo! I use Joomla 1.5 and now my site is down and I get this error message
jtablesession::Store FailedDB function failed with error number 1016
Can't open file: 'jos_session.MYI' (errno: 145) SQL=INSERT INTO `jos_session` ( `session_id`,`time`,`username`,`gid`,`guest`,`client_id` ) VALUES ( '4bc998b10d92bf4107976d0edacdbb26','1246725653','','0','1','0' )
My answer was:
If you have access to phpmyadmin, go to the Joomla database, select the table jos_session (tick the checkbox) and choose "Repair table" from the drop-down you find at the bottom of the list of tables. This has worked for me.
Step-by-step instructions
1. Log in to phpmyadmin on your database server
2. Go to the Joomla tables list for the database of your web site (select the database name in the left column drop-down menu)
3. Click the checkbox next to the jos_session table name (fig. 1)
4. At the bottom of the table, click 'Repair table' in the drop-down 'With selected' (fig. 2).
5. Your table is repaired (fig. 3)
This should solve the problem. However, sometimes this problem is caused by an extension or something else in your Joomla installation or on your server. Thus, the problem can reappear if you don't find the source of the problem. Sometimes I've had this happen because of spikes in traffic, though. In that case, you should monitor your site and perhaps invest in a service like Pingdom to keep track of uptime.
Good luck!
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