Reuben

there’s only one CSS file for this theme

and it should be style.css else it will show that error. If it is style.css check your error logs, file_exists function might be failing.

Check your error log, i think file_exists function is failing..

Make sure you have style.css and index.php in your theme folder.

I’m working on a custom theme for a client.

Is it a child theme?

Try this in command in console window( cmd.exe on windows )
ping www.yourdomain.com
You’ll get something like Pinging www.yourdomain.com [IP address]

How could I also make that slug the title for the page?

$wpdb->update( $wpdb->posts, array( 'post_name' => $custom_slug, 'post_title' => $custom_slug ), array( 'ID' => $post->ID ));

Try to manual update wordpress again( caution: don’t update the wp-content folder )

still now working.

I take it as “not”

Secondly, I use Windows Live Writer for posting content and images.

If you have not used media manager to upload the pictures, I don’t think the urls can change automatically.

Try refreshing your page, clear cache then delete the comment and refresh the page again.( I know it sounds lame )

Only error log is on my cPanel

Yep, thats the one.

performance pages

???

Huh…. can’t do that. Site would be unusable

In this case, you won’t be able to know if its the theme problem.

Anyways, check your error log to further debug the problem.

Try updating the permalink structure..

Also, if you have FTP’ed the images previously( on firstdomain ) the url can’t be changed automatically.

Have you tried reverting back to default 2010 theme??

Go to Media->Library to edit images( Its’ nothing like Photoshop/GIMP btw )