I just upgraded but instead of my blog, I see a white page. I can login to Admin just fine. After logging in, if I go to Presentation->Theme I see: Warning: array_keys() [function.array-keys]: The first argument should be an array in /usr4/u/1/psimmond/public_html/Blog/wp-includes/theme.php on line 298
If I select the Theme Editor tab, I get the same message and under it it says "The requested theme does not exist."
I deleted all of the old files before uploading the new ones.