I resurface an old post by me without reply.
The original post is here
I copy/paste the end :
Ever the same warning, today with WP 3.0.1 and WP SuperCache 0.9.9.6.
Maybe there is a mistake in the code of wp-cache.php ?
After the plugin is installed and works, when I display the advanced page in WPSC settings, I see ever the same warning : "Cannot update .htaccess".
(With .htaccess in 666, no warning. With .htaccess in 644, warning)
In wp-cache.php, the code is (line 1058) :
So, in any case (before or after update of .htaccess), there is a call to the function wpsc_update_htaccess_form().
In the body of this function (line 2290), there is in the beginning :
if( !is_writeable_ACLSafe( $home_path . ".htaccess" ) )...
And is_writeable_ACLSafe(/.../.htaccess) return ever false if I chmod
.htaccess to 644. But, for safety reasons, this file cannot stay in 666 (it's the .htacces on the root).
To fix this issue, I replace (line 72 in wp-cache.php, after the plugin is updated and working) :
if ($f===false) return false;
if ($f===false) return true;
But maybe it's not a definitive solution.