503 on site, manager works fine

While testing the new ModX 2.2.0-rc1 I have the following problem:

I always develop at my laptop and the upgrade to 2.2.0-rc1 went fine. When I place the site at my testserver, I can login in the manager and it works great. The site however, gives me a "Error 503 Site temporarily unavailable" error. I checked everything, from system specs (php/mysql/etc versions and module requirements) to .htaccess. I can't get it to work. I have no error in the managers error log, and not in the apache error log. My laptop and server both run linux (Ubuntu 11.10 and Debian stable). I also tried to delete all the files from the server and upload them again, but the problem exists...

Last but not least, the UI is definitely improved. I love it!

It sounds like you need to update your configuration some (core.config.php and database). Try re-running the setup.