Re: Changed theme, now can't get into site
I don't know specifically what's causing that error. It looks like the server can't create a cache directory for some reason. Normally, the Simple theme works fine and doesn't cause this kind of error. There seems to be something wrong with the server's file/directory permissions.
In the meantime, you can change your site's theme by access the database with phpMyAdmin or some other utility. Go to the tiki_preferences table and find the row where name = style and value = simple.css. Edit it by replacing simple.css with another theme name (including .css).
-- Gary