I had similar issues, with a white page, after upgrading my site to 2.0.15. I tried several solutions as described under different threads here, but I found another solution.

In MySQL I changed:
-> config
-> theme_set
-> conf_value to default

Then my site was up again. I havn't tried to change back to my old theme yet

I want two different themes on my site. One for desktop-users, and one theme for pda/mobile-users. The mobile-theme should not have sideblocks, and could have less content. Any idea how do this? I've been thinking of two different way to do it
1. Create a new xoops-site in the sub-domain, and use the same database at the content (how do I do this?)
2. Create a new theme, and have two themes to choose from. Then I need the subdomain to redirect to the pda-theme.

Could anyone help me?

Håvard