[Plugin: WP CleanFix] "Tables optimize" doing nothing?

Hello,
I like your plugin very much!

A question:
Why “Tables optimize” seems doing nothing? It says I have 38 of 38 with the red cross, but when I click Optimize! it goes ajax but returns to still the same state. Do I need to enable anything special at the DB?

Thanks!

http://wordpress.org/extend/plugins/wp-cleanfix/