Permalink rewriting in 3.0

See the category archive plugin FAQ.

To get the plugin to work with permalinks in WP3.1, you need to update the redirect_canonical() function in canonical.php. On line 167, wrap the following code:

$tax_url = parse_url($tax_url);
if ( ! empty($tax_url['query']) ) { // Custom taxonomies may only be accessable via ?taxonomy=..&term=..
    parse_str($tax_url['query'], $query_vars);
    $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
} else { // Taxonomy is accessable via a "pretty-URL"
    $redirect['path'] = $tax_url['path'];
}

in an if (is_tax()) block:

if (is_tax()) {
    $tax_url = parse_url($tax_url);
    if ( ! empty($tax_url['query']) ) { // Custom taxonomies may only be accessable via ?taxonomy=..&term=..
        parse_str($tax_url['query'], $query_vars);
        $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
    } else { // Taxonomy is accessable via a "pretty-URL"
        $redirect['path'] = $tax_url['path'];
    }
}

Thanks Hugh for your reply. I am using wp 3.1 so I changed the code as per above. in my .htaccess I have:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

My permalinks settings are:
/%category%/%year%/%monthnum%/%post_id%/%postname%/

Now when I click on a specific month I still don’t get the results I should, instead I kind of stay on the same page.
Any other suggestions?

Not sure, maybe clear your cache. I tried the same permalink structure you have

/%category%/%year%/%monthnum%/%post_id%/%postname%/

and it works for me. The month links should look something like

/category-label/2011/03/

Thank you Hugh, now it works !!!

I don’t know why it doesn’t work for me. ??
I wonder if it’s because I have category base set up as Categories in Permalinks settings?
i changed:

$tax_url = parse_url($tax_url);
if ( ! empty($tax_url['query']) ) { // Custom taxonomies may only be accessable via ?taxonomy=..&term=..
    parse_str($tax_url['query'], $query_vars);
    $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
} else { // Taxonomy is accessable via a "pretty-URL"
    $redirect['path'] = $tax_url['path'];
}

TO

if (is_tax()) {
    $tax_url = parse_url($tax_url);
    if ( ! empty($tax_url['query']) ) { // Custom taxonomies may only be accessable via ?taxonomy=..&term=..
        parse_str($tax_url['query'], $query_vars);
        $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
    } else { // Taxonomy is accessable via a "pretty-URL"
        $redirect['path'] = $tax_url['path'];
    }
}

BUT the problem is still there. does anybody have any other suggestions please?