I’m having the same problem – When I choose the alternate theme, it comes up on the screen ok – but if I leave here without doing anything else and go to my site, it is a blank page when I view it in Explorer.
So I went back to the Design/themes selector, choose the theme again and this time – when I got the screen with the image of my home page, I saw a grey area just above it – Mine says “Active your theme…” yours may say something different – Click on it – it’s a hyperlink that actually makes the change hold.
I hope this works for you.
