I have gone to them options and uploaded a 320×70 logo and it works for the basic demo content install. After I upload any other demo theme the logo will upload in theme options but will not load when the page renders. I have a completely fresh install uploaded via ftp – all plugins downloaded from your site.
Sorry, but to check the issue we need to see your site.
So please give us WP Dashboard and FTP credentials in private content (only our staff will see it, no any clients) and describe how to replicate the problem.