@tentblogger
I came across your problem too. For some reason something in the array for the minify settings has gotten messed up in the config file.
If you open your configuration file named “w3-total-cache-config-yoursitename.php” you will see a section for minify.css and minify.js
In there will be some arrays that should have locations of your minified files.
Make sure to disable Minify. Then delete only the arrays as shown below. Be careful not to delete anything else — like the beggining/ending array tags.
'c5082' => array(
'default' => array(
'include' => array(
'files' => array(
0 => 'wp-content/themes/mysite/style.css',
1 => 'wp-content/themes/mysite/js/colorbox/colorbox.css',
2 => 'wp-content/themes/mysite/skins/blue.css',
3 => 'wp-content/themes/mysite/custom.css',
4 => '/wp-content/plugins/sidebar-login/style.css?ver=3.1.3',
),
),
),
),
You should be left with these for each group.
'minify.css.groups' => array( ),
'minify.js.groups' => array( ),
Then go back and re-add your files and enable minify. That should fix your problem.