I can't customize my "Spirit" theme (or any upfront theme)

I got upfront, spirit and scribe installed on my multisite. It's a newly installed one, and it has only the main blog at the moment.
I'm trying to configure the theme, but to no avail.
Clicking "Upfront" pops up an alert which says: "please hold on for just a bit more".
Any idea why this happens? And how I can edit my themes?