I had the exact same problem, and I fixed it. It was the plugins. One of them was not compatible with WP 2.8.
VERY IMPORTANT: before you do a manual update on your site, you MUST deactivate ALL plugins. Then, turn them back on one at a time and refresh your site until it breaks. That will lead you to the plugin that’s causing the internal server error. What a pain ??
This plugin was the one that was causing the error for me:
https://www.bravenewcode.com/wptouch/
Hope this helps someone with the same issue.
