Tables start corrupting after myisamchk repair

I have a Invision 1.2 forum.
Linux Centos
PHP 4.3.9
MySql 4.1.20

The application has been running with no problems whatsoever for one year.

I wanted to “optimze” the tables to remove the overhead from deleted records. Big Mistake… that was the beginning of my problems.

I used PhpMyadmin to optimize all tables except two that were very large (2 million records).

I then shut down Mysql, and did a myisamchk repair on the two really large tables. No error were found or reported.

I then fired up MySqld and within an hour, started getting a corrupted table (errno 145). I shutdown mysql and once again ran myisamchk to repair the table. No errors are reported during the repair but a check before the repair does show that it was corrupted.

Ever since the initial PhpMyadmin optimize and the myisamchk repair on the large tables, I am getting a corrupted table within a few hours of running the forum.

There were no problems for over a year before I ran the initial optimization - after that, it is happening constantly.

Any ideas?? Need more info???

At wits end…